mta-park2021-1_Geotechnical report.pdf

158377846

M E M O R A N D U M Western Federal Lands Highway Division

610 E. Fifth Street

Vancouver, WA 98661

DATE:

TO:

FROM:

January 30, 2024; REVISED February 26, 2025

Wendy Schmidt, Project Manager

Orion George, Engineering Geologist Eric Lim, Sr. Geotechnical Engineer

SUBJECT: Geotechnical Memorandum GM0124 – REVISED Geotechnical Subsurface Investigation Results Old Yellowstone Trail South Improvements and Preservation MT FLAP Park 2021(1) Park County, Montana

INTRODUCTION

This memorandum has been REVISED to account for a reduction in the original scope of the project. The original scope was reduced from 13.3 miles of roadway to the first approximate 8.2 miles (Station 13+00 to Station 445+00). However, all geotechnical work completed under the original project scope is provided within this memorandum.

This memorandum provides findings from an October 2023 subsurface investigation along a portion of the Old Yellowstone Trail South (OYTS), completed by Western Federal Lands Highway Division’s (WFL) Geotechnical Function with the assistance of the Park County Public Works Department. Recommendations for design of cut slopes and embankments are included. Attachment A are maps of the project length and test pit locations.

PROJECT DESCRIPTION

The project is approximately 13.3 miles along the historic OYTS, a Park County, Montana maintained gravel-surface roadway, extending from near the Roosevelt Arch in Gardiner, Montana northwest through the entrance of Yankee Jim Canyon along the western bank of the Yellowstone River. The roadway is partially along the original wagon trail and the original railroad line into Yellowstone National Park (YNP).

The first 4.1 miles is within YNP, but traverses through private property and Custer-Gallatin National Forest for the remainder of its length. The OYTS connects with US Highway 89 further to the north; US Highway 89 is above the east bank of the Yellowstone River along most of the project length. It is our understanding scope of this project is to recondition gravel surfacing, raise grade elevations in select locations, formalize trailheads, install drainage culverts, and increase recreational and interpretive signage along the roadway. A peripheral goal of this project is to increase community access resiliency with improved emergency egress and ingress to the Gardiner, Montana area in case of closure of US Highway 89.

Currently, OYTS is closed due to embankment failures and rockfall within Yankee Jim Canyon. These failures are outside the scope of this project; and are being addressed via Federal Emergency Management Agency (FEMA) funding. June 2022 Yellowstone River flooding also impacted OYTS by flooding, depositing sediments, and further eroding riverbanks below the road.

Stationing used and provided in tables and location descriptions in this memorandum were provided by the WFL Design Function and are dated December 6, 2023. As stationing often changes, we provide latitude and longitude coordinates with certain items.

Previous Work

Field observations were made for a previous project that assessed development of a trail along the historic Old Yellowstone Trail railroad alignment. Orion George, WFL engineering geologist, and Nathan Jenks, WFL geologic engineer, conducted an Unstable Slope Management Program (USMP) survey of the area for the trail project May 7 to May 9 and May 21, 2018 (FHWA, 2024). Work completed for the trail project are outside of the limits of this project, but the USMP work is mentioned so future workers are aware of it. The USMP work is presented under cover of geotechnical memorandum GM1718.

A site visit was completed by Eric Lim, WFL geotechnical engineer, on January 13, 2023 to observe reported damage within Yankee Jim Canyon, also outside the limits of the project. His observations and recommendations are presented under cover of geotechnical memorandum

GM0623.

Another site visit was completed by Michael Chen, WFL materials engineer, on April 18, 2023 to observe site conditions. Michael provided notes, photographs, and observations to us, which informed our subsurface investigation and subsequent interpretations and recommendations. Michael also provided a preliminary aggregate design memorandum dated October 20, 2023.

GEOLOGY

Geology of the project area has been mapped by Berg et al. (1999) at the 1:100,000 scale.

The project traverses largely unconsolidated alluvial sediments deposited by fluvial (river) or glacial processes. The alignment also crosses three large landslides mapped by Berg et al.

(1999), and also more recently by Nicholas (2018). Attachment A.6 and A.7 are geologic maps of the project vicinity.

Along the project glacial deposits are mapped as undivided (map symbol Qg) and likely mostly unconsolidated sediments associated with deposition from glacial outwash (glacial melt waters) and glacial outburst flooding. Some glacial till, deposits over-consolidated by glacial ice weight, may also be present, although we did not observe it during our field visits. The Qg deposits are described as being unsorted and unstratified, but along the project length deposits and landforms resemble deposition via fluvial processes, with soils often sorted and stratified. Sorting and stratification yield information on how much energy water was available during sediment deposition. Hence, areas of glacial outburst flood deposits would be expected to have larger boulders and generally coarser grained sediments than glacial outwash deposits or mapped alluvium (map symbol Qal), both of which are deposited by riverine systems.

The alluvium, Qal, unit is younger than glacial deposits. Both glacial outwash deposits and Qal would be expected to have more fine-grained fractions within their sediments due to expected relatively lower energy depositional environments than a glacial outburst flood.

Landslide deposits (map symbol Qls) are typically unstratified and unsorted as their soils have been deposited by movement from a higher elevation to a lower elevation, a generally disorderly method of deposition. Berg et al. (1999) shows a large landslide in the vicinity of Cutler Lake, approximately station 549+00 to about station 624+00. More recent surficial mapping was also consulted, which had mapped additional landslides at the beginning of the project (Nicholas, 2018). One landslide just barely enters the project limits at the beginning of the project and the alignment crosses the other from approximately station 36+60 to about station 104+00. Attachments A.2, A.6, and A.7 show mapped landslides in relation to the project.

Consulted geologic mapping fits field observations along the project length. Typically, larger boulders were observed at the beginning of the project and within the mapped glacial units.

Further up station sediments generally have a higher fine-grained fraction, which correlates with areas mapped as alluvium. The landslide mapped near Cutler Lake is an outlier as soils along this stretch have more cobbles and boulders in combination with fine grained soils.

Geologic Hazards

Outside of having mapped landslides along the project, no issues were noted associated with other unstable slopes. Park County Public Works did not provide any information suggesting sections of road crossing mapped landslides are being impacted by deep-seated landslide movement and we interpret these features as very slow moving or inactive. Further, the recent surficial work by Nicholas (2018) mapped landslides at the beginning of the project within YNP. Using lidar topographic data from 2010, Nicholas analyzed surface roughness of her mapped landslides to assess relative landslide age. Nicholas considered the landslides near the project to be older and less active to inactive.

We feel geologic hazards with higher risk of impacting OYTS are flooding and related erosion.

The roadway was overtopped and had significant depths of sediment deposited on it in numerous locations from the June 2022 flood event. This flood also caused significant bank erosion and loss of bank riprap revetment, specifically ranging approximately from station 460+20 to station 479+20. However, it is our understanding since our subsurface investigation in October 2023 Park County has placed additional riprap along this stretch to protect from further bank erosion.

Additionally, the revetment site (about station 460+20 to 479+20) and an area near the end of the project, from station 546+60 to 689+00, were flooded during the June 2022 flood, a 500+ year event that impacted the area greatly. The inundation of these two areas deposited a significant amount of sand and silt, up to about 10 feet depth was reported to us by Park County. Much of the flood deposit was hauled away by Park County or blown away by winds, but some flood deposits were still recorded at test pit sites (SG23-06 and SG23-10).

SITE CONDITIONS

The project’s site conditions were greatly informed by high resolution aerial lidar data collected in fall of 2020 (USGS, 2021). This data acquisition was collected at quality level 2 (QL2), a 1 meter (3.3 feet) horizontal resolution and 10 centimeter (3.9 inch) vertical resolution. Hillshade derivatives of these data are viewed on maps in Attachment A.

The project roadway is generally a low gradient, approximately 25-foot wide, aggregate surfaced road. Vegetation is sparse along the alignment and typically made up of grasses and sagebrush, although along higher elevation areas or when crossing streams juniper, lodgepole pine, Douglas fir, quaking aspen, and cottonwood can be seen. The road also traverses several older and active agricultural fields. Representative site photographs are available in Attachment B.

One location differing from the above description is where the OYTS climbs up and over the landslide that Cutler Lake is on (Cutler Lake landslide). Along this stretch of the road the gradient increases and becomes notably more sinuous as it climbs over the Cutler Lake landslide deposit. More trees and shrubs are seen along this section of the project as well with numerous boulders, up to at least 6 feet in dimension, along the roadway.

Numerous areas along the roadway exhibited potholes, wash-boarding, and rutting with the most severe areas between approximately station 489+00 to 622+00. This area also exhibited muddy surface conditions suggesting drainage is a challenge as well. Michael Chen also communicated the area between approximate stationing 489+00 to 622+00 exhibited the worst surface conditions “from a materials engineer’s perspective”.

FEMA 100-year flood mapping was consulted to review and assess risk to flooding of OYTS (FEMA, 2024). These maps are developed to inform the risk of flooding in areas, with areas inside of the 100-year flood zone having a 1% chance or higher in experiencing a flood each year, or a one-in-four chance of flooding every 30 years. This mapping highlights two areas along the project within the mapped 100-year flood polygon along the roadway at approximate stationing 465+00 to 478+00 (flood site 1; Attachment A.4) and 667+00 to 699+00 (flood site 2; Attachment A.5). Both areas were inundated by the June 2022 flood, a 500+ year event, although we are uncertain by how much flood waters covered the sites. It has also been communicated to us that flood site 2 has been inundated often at lower flood levels, but we are not sure of that level. It should also be noted the FEMA 100-year flood mapping was done before the June 2022 flooding and current channel conditions have changed due to the major flood event. Therefore, current conditions differ from when FEMA mapping was completed.

Flood site 1 has the 100-year flood boundary mostly along the road at about an elevation of 5,090 feet; about 3 feet over the road elevation. Flood site 2 is within the mapped flood zone to a greater extent and mapped approximately elevation 5,050 feet suggesting the current road would be under water approximately 3 feet for a modeled 100-year flood event as well.

It should be stressed no hydraulic modeling was completed for this work and estimated elevations of 100-year flood height over the current road elevation is limited by the resolution of FEMA’s 100-year flood map, which was modeled before the major June 2022 flood event and the current high resolution aerial lidar acquired in 2022. Hydraulic Engineers should be consulted for a full assessment of flood levels and risk along this alignment.

SUBSURFACE CONDITIONS

A subsurface investigation was conducted to better characterize conditions along the project length. The WFL Materials Function was consulted in development of the subsurface investigation to better inform their recommendations as well.

Eleven test pits were dug with a CAT 416E backhoe by Park County Public Works along OYTS October 17 and 18, 2023. Orion George, WFL engineering geologist, was on site to log test pits and sample materials for testing by the WFL Materials Laboratory. Table 1 summarizes subsurface explorations performed by project stationing, latitude and longitude coordinates, roadway surfacing depth, and main purpose. Test pit locations can be viewed in Attachment A, test pit site photographs are in Attachment B, test pit logs are available as Attachment C, and WFL Materials Laboratory testing results are available in Attachment D.

Table 1 Test pits location by project station, GPS coordinates, elevation, depth, road surfacing thickness, and main purpose of test pits.

Test Pit Station1 Latitude (deg N)2

Longitude (deg W)2

Elevation (ft)2

Depth (ft)

Road Surface Thickness (ft) Main Purpose

SG23-01 16+67 45.0317 -110.7152 5,273 3.0 0.5 Subgrade

SG23-02 122+45 45.0449 -110.7500 5,243 3.0 0.4 Subgrade

SG23-03 228+49 45.0639 -110.7748 5,201 2.8 0.3 Subgrade

SG23-04 334+00 45.0919 -110.7838 5,203 3.1 0.4 Subgrade

SG23-05 439+54 45.1176 -110.7996 5,106 3.4 0.3 Subgrade

SG23-06 466+07 45.1244 -110.8029 5,087 5.0 0.0 Grade raise

SG23-07 514+83 45.1353 -110.8128 5,138 3.2 0.8 Subgrade

SG23-08 682+17 45.1520 -110.8264 5,311 3.6 0.3 Subgrade

SG23-09 588+08 45.1635 -110.8474 5,053 6.1 0.4 Grade raise

SG23-10 662+88 45.1647 -110.8506 5,051 5.3 0.0 Grade raise

SG23-11 672+12 45.1662 -110.8537 5,051 6.5 0.2 Grade raise

Note:

1) Stationing from designs received 12/6/2023.

2) Coordinates and Stationing are approximate. Coordinates and elevations were estimated using GPS location and lidar data in the North American Datum (NAD) 1983 National Readjustment (NSRS2007) geographic coordinate system. Stationing dated 12/6/2023.

Conditions observed in test pits suggest soils are coarser grained near the project beginning and have a higher fine fraction further to the north. More coarse sand, gravel, and cobbles with boulders were observed on the surface and in the test pits from the beginning of the project to approximately station 250+00. The area where the roadway traverses Cutler Lake landslide also has a higher coarse-grained fraction, but it also appears to be in a unsorted mixture of fine sediment as well, as expected with a landslide deposit. These observations fit referenced geologic mapping and surficial observations described above.

As all test pits were dug within the roadway topsoil was not directly measured, but considering local climate and vegetation shallow topsoil throughout the project length is anticipated and expected not to exceed more than 2 inches of thickness. Current road gravel surfacing was measured in test pits and varied, but generally a thin road surfacing was observed and reported in Table 1. The gravel road surfacing was typically a well graded SAND with angular to subangular gravel, but notably two sites did not have observable road surfacing (SG23-06 and SG23-10), which had alluvial deposits covered by recent flood deposits from the June 2022 flooding. Both of these sites are within the mapped 100-year FEMA flood zone and appear to have been impacted by even older flood deposition. No base layer was observed below the gravel road surfacing and was often considered a poor subgrade material: poorly graded sand with silt to a silt. Full test pit stratigraphy is provided in the test pit logs located in Attachment B.

No groundwater was observed at the time of our subsurface investigation. However, water levels and/or conditions may vary considerably, with time, according to climate, season, precipitation, and other factors.

DESIGN RECOMMENDATIONS

The following recommendations stem from work prioritization from Park County and observations made during site visits, from test pits, material test results, and our professional experience.

It is our understanding Park County has prioritized work along the project length during a partner meeting on January 19, 2024. Park County’s prioritization was given to us in the order below:

1. Roadway reconditioning from the project beginning, near Gardiner, to the Beattie Gulch Trailhead, approximately station 16+00 to 230+75.

2. Roadway reconditioning from Beattie Gulch Trailhead to the Corwin Springs Bridge, approximately station 230+75 to 411+00.

3. Raise grade in the section before Yankee Jim Canyon to a 2-year rainfall event elevation, approximately station 647+00 to 679+00.

4. Roadway reconditioning from Corwin Spring Bridge to near Cutler Lake, approximately station 459+00 to 468+00.

We provide the following recommendations while considering the above prioritizations provided by Park County.

Michael Chen, WFL materials engineer, provided a preliminary aggregate surface design in a memorandum dated October 20, 2023. Recommended preliminary aggregate design is 6 inches thickness of Aggregate Surface Course over 6 inches thickness of Aggregate Base Grading D (FP-14, Section 301). It is possible data included in this memorandum will result in a revision to the Materials recommendations.

Subgrade soils were observed to be coarse from the project beginning to approximately station 454+00. We anticipate minimal mixing of the upper aggregate surfacing with subgrade materials will occur through this section of the roadway. This section of roadway includes both Park County’s priorities #1 and #2 from above. We also recommend improvements to ditches and culverts throughout this section to improve positive drainage from the roadway, which will benefit the alignment’s driving surface and subgrade longevity.

Due to observed increases in higher soil fine fractions from approximately station 454+00 toward the end of project we feel there is a higher chance of aggregate surfacing materials mixing into subgrade materials below. With this in mind, we recommend considering a more robust aggregate surface design, whether it be a thicker aggregate design or the inclusion of geotextile separation and stabilization material into the design. It should be noted, while including a separation and stabilization geotextile over subgrade material and below the aggregate surface design would reduce the possibility of mixing subgrade materials with surface materials and increase overall strength and rigidity of the aggregate surface course, it would also introduce higher material costs and a risk over time of fabric being exposed during future grading operations. As such, we do not recommend the use of a separation and stabilization geotextile product in this section of the project unless the geotextile can be placed at least 8 inches below the road surface. A portion of Park County’s #3 priority is within this part of the project. We also recommend improvements to ditches and culverts throughout this section as well to improve positive drainage from the roadway, which will benefit the driving surface and subgrade longevity.

Embankments and Fills

In areas of anticipated embankment construction, we recommend soil embankment slopes be designed at a 1V:2H to 1V:1.5H slope. We recommend maintaining a 1V:2H slope as it is harder to establish vegetation on steeper slopes. If slopes steeper than 1V:1.5H are needed a special rock embankment (SRE; FP-14, Section 252) can be used to design slopes up to 1V:1.25H. If even steeper slopes are required other options can be considered such as a reinforced soil slope (RSS; FP-14, Section 261), which can provide a slope from 1V:1.5H to 2V:1H.

It should be noted some settlement over time may occur with placement of embankment over soft soil areas. However, since the roadway is aggregate surfaced, no special mitigation for settlement is deemed necessary other than completing the placement of the embankment as early in the project as possible, and fine grading these areas at least one month after completion of the embankment. This time period should allow for the majority of subgrade consolidation to occur. A geotextile stabilization fabric or stabilization geogrid with a separator fabric should be planned for soft subgrade areas The placement of the geotextile stabilization fabric or stabilization geogrid will reduce the amount of over-excavation needed during construction to obtain a stable subgrade for fill placement.

Cut Slopes

In areas planned for slope cutting we recommend slopes to remain below 1V:1.75H. Again, steeper slopes are more challenging to re-establish vegetation. As with embankment slopes, discussed above, if steeper slopes are required a rockery or other retaining structure may be required.

Grade Increases

In general, we recommend the roadway be designed to raise grade slightly to take advantage of the existing roadway surfacing, where it exists. This will also reduce the chance of encountering softer subgrade soil units, which can make re-compaction challenging, particular if higher or lower moisture contents than optimum are present. Removal of surficial June 2022 flood deposits are recommended when encountered before placement of aggregate base and surface materials. This is expected to occur in two locations from approximately station 465+00 to 478+00 and 650+00 to the end of project.

To maintain a resilient roadway for emergency traffic (in case of a Highway 89 closure) we recommend addressing the roadway elevation of the alignment within approximate stationing 465+00 to 478+00 (flood site 1) and 667+00 to the end of the project (flood site 2). Currently both sections are partially within the FEMA 100-year flood zone. Both areas were also inundated by June 2022 flood waters. Flood site 2 is Park County’s third priority. We recommend any increase in elevation will at both sites improve resiliency to flooding, but flood site 2 is more susceptible than flood site 1. As such even a 1- to 2-foot increase in elevation at flood site 2 is anticipated to be an improvement. The WFL Hydraulic Engineering Function should be consulted to ascertain what elevation a 2-year flood event would be for both flood sites.

CONSTRUCTION CONSIDERATIONS

Based on field observations boulders and cobbles are likely to be encountered in excavations along this alignment, with more likelihood in the beginning of the project to about station 400+00 and from station 542+00 to 624+00. Boulder dimensions up to 10 feet were observed on the surface near the alignment. The contractor should be prepared to use equipment of sufficient size and outfitted appropriately to handle boulders of similar size as can be observed on the surface.

Considering the high silt content in subgrade materials, particularly in the latter portion of the project length, we recommend avoiding cuts or subexcavation in times of wet weather, expected wet weather, and/or seasonally wet conditions. Soils should be allowed to drain and dry sufficiently after snow melt-off in the spring before any excavation operations are begun.

Further, efforts should be made to control surface waters and prevent directing runoff into construction sites. The use of temporary berms and/or trenches, erosion control best management practices, and stage construction methods could be utilized as needed and determined by the contractor. Seepages could be encountered in any excavation, and the contractor should be prepared to divert the water around or through the excavation area.

Based on material testing results and field observations of encountered surficial and subsurface soils, onsite soils are generally not considered suitable for reuse within the roadway as fill or for use in embankment construction, since most cut areas will likely be in soft, silty subgrade areas or recent flood deposits. Testing of materials is required at the time of construction, and the responsibility of the contractor, if onsite materials are to be considered for use on the project. Surface and subsurface rights of all materials planned for use must be verified by the contractor prior to use on the project.

LIMITATIONS

This memorandum has been prepared to assist WFL with the engineering design and constructability of the Old Yellowstone Trail South Improvements and Preservation project. It should not be used, in part or in whole for other purposes without contacting the WFL Geotechnical Function for a review of the applicability of such reuse. These data are not to be used for other purposes.

Conclusions and recommendations contained in this report are based on WFL’s Geotechnical Function’s understanding of the project at the time this memorandum was written and onsite conditions that existed at the time of field observations and subsurface investigation. If significant changes to the nature, configuration, or scope of the project occur during the construction phase of work, the Geotechnical Function should be consulted to determine the impact of such changes on our final geotechnical recommendations and conclusions presented in this memorandum.

Subsurface investigation and associated laboratory testing describe subsurface conditions only at sites of subsurface investigation and at intervals samples were collected. These data are interpreted by members of the WFL Geotechnical Function, who then render a professional geotechnical opinion regarding general subsurface conditions. Distribution, continuity, thickness, and characteristics of identified (and unidentified) subsurface materials may vary considerably from that indicated by observed and interpreted subsurface data. No groundwater was observed at the time of our subsurface investigation, however, water levels and/or conditions may vary considerably, with time, according to climate, precipitation, and other factors and are otherwise dependent on duration of, and methods used in, and interpretations made from the subsurface investigation.

REFERENCES

Berg, R.B., J.D. Lonn, and W.W. Locke, 1999, Geologic map of the Gardiner 30’ x 60’ Quadrangle, south-central Montana, Montana Bureau of Mines and Geology.

Federal Emergency Management Agency (FEMA), 2024, National Flood Hazard Layer, database for the United States: https://www.fema.gov/flood-maps/national-flood-hazard-layer, accessed January 19, 2024.

https://www.fema.gov/flood-maps/national-flood-hazard-layer https://www.fema.gov/flood-maps/national-flood-hazard-layer

Federal Highway Administration (FHWA), 2024, Unstable Slope Management Program (USMP), https://highways.dot.gov/federal-lands/geotechnical, accessed January 10, 2024.

Nicholas, G.E., 2018, Landside morphology and its insight into the causes of slope failure: A case study of post-glacial landslides in Yellowstone National Park, Master’s Thesis, Montana State University.

United States Geological Survey (USGS), 2021, Lidar mapping report for “WY Yellowstone NP 2020 D20” aerial lidar acquisition, dated April 2021, https://apps.nationalmap.gov/lidar-explorer/#/, accessed May 8, 2023.

CLOSING

Please contact ORION GEORGE (360-619-7634 or Orion.George@dot.gov) or ERIC LIM (360-619-7826 or Eric.Lim@dot.gov) with any questions regarding this memorandum.

CC: Tyler Yeoman, WFL Highway Designer

Jenn Mora, WFL Hydraulic Engineer Benjamin White, WFL Environmental Protection Specialist Michael Chen, WFL Materials Engineer Geotechnical File

Attachment A: Map A.1: Project Overview Map Map A.2: Test Pit Locations Map #1 Map A.3: Test Pit Locations Map #2 Map A.4: Test Pit Locations Map #3 Map A.5: Test Pit Locations Map #4 Map A.6: Geologic Map #1 Map A.7: Geologic Map #2 Attachment B: Site Photographs Attachment C: Test Pit Logs Attachment D: Materials Testing Results https://highways.dot.gov/federal-lands/geotechnical https://apps.nationalmap.gov/lidar-explorer/#/ mailto:Orion.George@dot.gov mailto:Eric.Lim@dot.gov

Attachment A

Map A-1: Project Overview Map Map A-2: Test Pit Locations Map #1 Map A-3: Test Pit Locations Map #2 Map A-4: Test Pit Locations Map #3 Map A-5: Test Pit Locations Map #4 Map A-6: Geologic Map #1 Map A-7: Geologic Map #2

Gardiner, MT

Y e l l o w s t o n e N a t i o n a l P a r k

G a l l a t i n - C u s t e r N a t i o n a l F o r e s t

660 640

170 150

Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), (c) OpenStreetMap contributors, and the GIS User Community

Map A.2

Map A.3

Map A.4

Map A.5

Legend Project Alignment

Centerline !( Stationing

Roads US Highway 89

Arterial roads

USFS

NPS

Map A.1: Overview

¹0 0.8 1.60.4 Miles

&D

&D

&D

Gardiner, MT

US Hwy 89

Yellowstone River

SG23-02

SG23-01

Legend Test Pits

&D SG23-01

Project Alignment Centerline

!( Stationing

Landslides (Nicholas. 2018)

FEMA 100 year flood elevation

Roads US Highway 89

Arterial roads

USFS

NPS

Map A.2

¹0 1,100 2,200550 Feet

&D

&D

US Hwy 89

US Hwy 89

YellowstoneRiver

SG23-04

SG23-03

Legend Test Pits

&D SG23-01

Project Alignment Centerline

!( Stationing

FEMA 100 year flood elevation

Roads US Highway 89

Arterial roads

USFS

NPS

Map A.3

¹0 1,100 2,200550 Feet

&D

&D

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Corwin Springsbridge

YellowstoneRiver

US Hwy 89

SG23-07

SG23-06

SG23-05

64006600

Legend Test Pits

&D SG23-01

Project Alignment Centerline

!( Stationing

FEMA 100 year flood elevation

Roads US Highway 89

Arterial roads

USFS

NPS

Map A.4

¹0 700 1,400350 Feet

Flood site #1 Flood site #1

&D

&D

&D

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G a l l a t i n - C u s t e r

N a t i o n a l F o r e s t

YellowstoneRiver

US Hwy 89

Yankee JimCanyonentrance

CutlerLake

SG23-08

SG23-11

SG23-10

SG23-09

&D SG23-01

Project Alignment Centerline

!( Stationing

FEMA 100 year flood elevation

Roads US Highway 89

Arterial roads

USFS

NPS

Map A.5 Legend Test P its

¹0 1,000 2,000500 Feet

Flood site #2 Flood site #2

Gardiner, MT

Qg

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Legend Project Alignment

Centerline !( Stationing

Landslides (Nicholas. 2018)

Roads US Highway 89

Arterial roads

Map A.6: Geology

¹0 0.45 0.90.225 Miles

Geology from Berg et al., 1999

G a l l a t i n - C u s t e r

N a t i o n a l F o r e s t

CutlerLake

Qls

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Legend Project Alignment

Centerline !( Stationing

Landslides (Nicholas. 2018)

Roads US Highway 89

Arterial roads

Map A.7: Geology

¹0 0.25 0.50.125 Miles

Geology from Berg et al., 1999

Attachment B

Test Pit Photographs

Attachment B 1 Photograph of test pit SG23-01 looking north. Note the wash boarding.

Attachment B 2 Photograph of test pit SG23-01 western wall.

Attachment B 3 Photograph of site SG23-02 looking north. Note boulder in background and potholing.

Attachment B 4 Photograph of test pit SG23-03 looking south. Note cobbles encountered.

Attachment B 5 Photograph of test pit SG23-03’s west wall.

Attachment B 6 Photograph of test pit SG23-04 looking south. The alignment is traversing active agricultural fields in this location.

Attachment B 7 Photograph of test pit SG23-04’s western wall.

Attachment B 8 Photograph of test pit SG23-05 looking north. Note cobbles within the excavated material.

Attachment B 9 Photographs of test pit SG23-05’s western wall.

Attachment B 10 Photograph of site SG23-06 looking north. Note the fine silty sand flood deposit material from the June 2022 flooding on the surface and moisture from the previous weeks rains. The Yellowstone River is in the right of the photo.

Attachment B 11 Photograph of site SG23-06 looking north. Note the rip rap off the shoulder edge of the road along the bank of the Yellowstone River.

Attachment B 12 Photograph of test pit SG23-06’s west wall.

Attachment B 13 Photograph of test pit SG23-08, looking north. The arrow points out a petrified log with surrounding volcanic ash encountered in the test pit.

Attachment B 14 Photograph of test pit SG23-09. This site encountered the finest sediment along the alignment. Note the dark layers in the middle of the test pit, which had approximately 2% organic content.

Attachment B 15 Photograph of test pit SG23-10.

Attachment B 16 Photograph of test pit SG23-11’s western wall. Clean, dry, fine sand was encountered within this test pit overlying a loose clean fine to coarse gravel with sand (see Attachment B17).

Attachment B 17 Photograph of the clean, dry fine sand encountered in test pit SG23-11. This material was being drained by a gravel layer below it.

Attachment C

Test Pit Logs

(6" = 100%)

(3" = 100%)

(12" = 100%)

(3" = 100%)

G02

M01

G01

M02

Well graded SAND with gravel, medium dense, brown, dry, angular to rounded, ROAD SURFACING.

0.5 ft / El. 5272.5 ft Poorly graded SAND with silt and gravel, medium dense, brown, moist, fine sand, rounded, gravel approximately 15% with clasts up to 3". Clay rich clumps observed at bottom of pit with roots. ALLUVIAL DEPOSIT.

3 ft / El. 5270 ft Bottom of test pit at 3 ft.

D ril lin g

M et ho d

Field Blow Count (Recovery)No.

T yp e

Test Results

SAMPLE

SG23-01

Sheet: 1 of 1

Project Location: Park County, Montana

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Old Yellowstone Trail South, MT FLAP Park 2021(1)

E le va tio n (f t)

D ep th ft)

MATERIAL DESCRIPTION

TEST PIT LOG

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

L O

G

F H

W A

_D A

T A

T E

M P

LA

T

E .G

D T

/2 3/

:2

D :\O

Y T

S \O

Y T

S _2

_T E

S T

_P

IT

S .G

P J

Groundwater Depth:

Notes:

After Drilling: ---

While Drilling: --- At Completion: ---

Fiber optic 6" under surface, northern shoulder. Test pit on south bound side of road.

Surface Elevation: 5273 ft Datum: MSL Latitude: 45.0317° Longitude: -110.7152° Datum: WGS84

Weather: Sunny

Date Started: 10/17/23 Date Completed: 10/17/23 Driller/Company: Cory Thornton/Park Cty Public Works

Logger/Company: Orion George/WFLHD

Equipment CAT 416E Approx. Excavation Dimensions: 2.5' x 4'

G ra ph ic

L og

(3" = 100%)

(3" = 100%)

G01

G01

M01

M02

Poorly graded SAND with silt and gravel, medium dense, brown, dry, fine sand to coarse sand, angular to rounded, clasts up to 3" with boulders up to 6' observed on the surface. ROAD SURFACING.

0.4 ft / El. 5242.6 ft Poorly graded SAND with silt, medium dense, brown, moist, fine sand to medium sand, subrounded to rounded, some lamination and cross-bedding observed. GLACIAL

OUTWASH.

1.2 ft / El. 5241.8 ft Poorly graded SAND with gravel, medium dense, brown, moist, medium sand to coarse sand, subrounded to rounded, clasts up to 4"; no silt. GLACIAL OUTWASH.

3 ft / El. 5240 ft Bottom of test pit at 3 ft.

D ril lin g

M et ho d

Field Blow Count (Recovery)No.

T yp e

Test Results

SAMPLE

SG23-02

Sheet: 1 of 1

Project Location: Park County, Montana

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Old Yellowstone Trail South, MT FLAP Park 2021(1)

E le va tio n (f t)

D ep th ft)

MATERIAL DESCRIPTION

TEST PIT LOG

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

L O

G

F H

W A

_D A

T A

T E

M P

LA

T

E .G

D T

/2 3/

:2

D :\O

Y T

S \O

Y T

S _2

_T E

S T

_P

IT

S .G

P J

Groundwater Depth:

Notes:

After Drilling: ---

While Drilling: --- At Completion: ---

Test pit on north bound side of road. Near an old borrow pit.

Surface Elevation: 5243 ft Datum: MSL

Weather: Sunny

Date Started: 10/17/23 Date Completed: 10/17/23 Driller/Company: Cory Thornton/Park Cty Public Works

Logger/Company: Orion George/WFLHD

Equipment CAT 416E Approx. Excavation Dimensions: 2.5' x 5'

G ra ph ic

(12" = 100%)

(3" = 100%)

G01

M01

M02

Well graded SAND with silt and gravel, medium dense, brown, moist, fine sand to coarse gravel, subrounded to angular, ROAD SURFACING.

0.3 ft / El. 5200.7 ft Poorly graded SAND with silt and gravel, medium dense, brown, moist, fine sand to coarse sand, rounded to subangular, cobbles up to 15" observed. GLACIAL

OUTWASH.

2.8 ft / El. 5198.2 ft Bottom of test pit at 2.8 ft.

D ril lin g

M et ho d

Field Blow Count (Recovery)No.

T yp e

Test Results

SAMPLE

SG23-03

Sheet: 1 of 1

Project Location: Park County, Montana

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Old Yellowstone Trail South, MT FLAP Park 2021(1)

E le va tio n (f t)

D ep th ft)

MATERIAL DESCRIPTION

TEST PIT LOG

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

L O

G

F H

W A

_D A

T A

T E

M P

LA

T

E .G

D T

/2 3/

:2

D :\O

Y T

S \O

Y T

S _2

_T E

S T

_P

IT

S .G

P J

Groundwater Depth:

Notes:

After Drilling: ---

While Drilling: --- At Completion: ---

Test pit on south bound side of road.

Surface Elevation: 5201 ft Datum: MSL

Weather: Sunny

Date Started: 10/17/23 Date Completed: 10/17/23 Driller/Company: Cory Thornton/Park Cty Public Works

Logger/Company: Orion George/WFLHD

Equipment CAT 416E Approx. Excavation Dimensions: 2.5' x 6'

G ra ph ic

(8" = 100%)

(12" = 100%)

(3" = 100%)

M01

G01

G02

M02

Well graded SAND with gravel, medium dense, brown, dry to moist, fine sand to medium sand, angular to subangular, clasts up to 1". ROAD SURFACING.

0.4 ft / El. 5202.6 ft Poorly graded SAND with silt, medium dense, brown with black and dark gray, moist, fine sand, angular to subangular, cobbles up to 1.2' observed. Black and dark gray, reported as coke from historic mining and railroad operations. OLDER ROAD SURFACING?.

1.8 ft / El. 5201.2 ft SILT with sand, firm, orangish brown, moist, subangular to rounded, sand mostly fine grained with medium to coarse sand and some gravel with clasts up to 3".

GLACIAL OUTWASH.

3.1 ft / El. 5199.9 ft Bottom of test pit at 3.1 ft.

D ril lin g

M et ho d

Field Blow Count (Recovery)No.

T yp e

Test Results

SAMPLE

SG23-04

Sheet: 1 of 1

Project Location: Park County, Montana

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Old Yellowstone Trail South, MT FLAP Park 2021(1)

E le va tio n (f t)

D ep th ft)

MATERIAL DESCRIPTION

TEST PIT LOG

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

L O

G

F H

W A

_D A

T A

T E

M P

LA

T

E .G

D T

/2 3/

:2

D :\O

Y T

S \O

Y T

S _2

_T E

S T

_P

IT

S .G

P J

Groundwater Depth:

Notes:

After Drilling: ---

While Drilling: --- At Completion: ---

Underground utilites noted off both shoulders of road. Test pit on north bound side of road.

Surface Elevation: 5203 ft Datum: MSL

Weather: Sunny

Date Started: 10/17/23 Date Completed: 10/17/23 Driller/Company: Cory Thornton/Park Cty Public Works

Logger/Company: Orion George/WFLHD

Equipment CAT 416E Approx. Excavation Dimensions: 2.5' x 5'

G ra ph ic

G01

M01

G02

M02

Fines = 30% Moisture content 9.1%

Well graded SAND with silt and gravel, medium dense, greyish brown, moist, fine sand to coarse sand, angular to subangular, ROAD SURFACING.

0.3 ft / El. 5105.7 ft Poorly graded SAND with silt, medium dense, brown, moist, fine sand to coarse sand, subangular to angular, clasts up to 3". OLDER ROAD SURFACING.

0.9 ft / El. 5105.1 ft Silty SAND (SM), medium dense, light brown, moist, fine sand to medium sand, rounded to subrounded, non plastic, sand mostly fine to medium grained, some coarse sand and fine to coarse gravel; clasts up to 1". Roots within soil unit. ALLUVIAL FAN DEPOSIT [AASHTO:

A-2-4 (0)].

1.9 ft / El. 5104.1 ft SILT with sand, firm, orangish brown, moist, rounded to subrounded, sand mostly fine grained with minor medium to coarse sand. Fining downward trend. ALLUVIAL

DEPOSIT.

3.0': Phone line encountered, not damaged; measured phone location 13.0' from nearby fence line. Hand dug pit to 3.6' below ground surface.

3.4 ft / El. 5102.6 ft Sandy lean CLAY, firm, light brown, moist, silt and fine sand within soil unit. ALLUVIAL DEPOSIT.

3.6 ft / El. 5102.4 ft Bottom of test pit at 3.6 ft.

D ril lin g

M et ho d

Field Blow Count (Recovery)No.

T yp e

Test Results

SAMPLE

SG23-05

Sheet: 1 of 1

Project Location: Park County, Montana

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Old Yellowstone Trail South, MT FLAP Park 2021(1)

E le va tio n (f t)

D ep th ft)

MATERIAL DESCRIPTION

TEST PIT LOG

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

L O

G

F H

W A

_D A

T A

T E

M P

LA

T

E .G

D T

/2 3/

:2

D :\O

Y T

S \O

Y T

S _2

_T E

S T

_P

IT

S .G

P J

Groundwater Depth:

Notes:

After Drilling: ---

While Drilling: --- At Completion: ---

Test pit 7' from north bound edge of road.

Surface Elevation: 5106 ft Datum: MSL

Weather: Sunny

Date Started: 10/17/23 Date Completed: 10/17/23 Driller/Company: Cory Thornton/Park Cty Public Works

Logger/Company: Orion George/WFLHD

Equipment CAT 416E Approx. Excavation Dimensions: 2.5' x 6'

G ra ph ic

(5" = 100%)

(6" = 100%)

(3" = 100%)

(4" = 100%)

M01

G01

G02

M02

G03

Fines = 24% Moisture content 9.7%

Fines = 52%

Fines = 94% Moisture content 34.2%

Poorly graded SAND, very loose, brown, moist, fine sand, clasts mostly fine sand with some silt. RECENT FLOOD DEPOSIT (June 2022).

0.8 ft / El. 5086.2 ft Silty SAND with gravel (SM), medium dense, brown, moist, fine sand to medium sand, rounded to subangular, non plastic, some coarse sand and fine to coarse gravel up to 5". ALLUVIAL DEPOSIT [AASHTO: A-2-4 (0)].

2.3 ft / El. 5084.7 ft Sandy SILT (ML), firm, brown, moist, fine sand, non plastic, some clay. ALLUVIAL DEPOSIT [AASHTO: A-4 (0)].

4.3 ft / El. 5082.7 ft SILT (ML), firm, light brown, moist, medium plasticity, ALLUVIAL DEPOSIT [AASHTO: A-7-6 (19)].

5 ft / El. 5082 ft Bottom of test pit at 5 ft.

D ril lin g

M et ho d

Field Blow Count (Recovery)No.

T yp e

Test Results

SAMPLE

SG23-06

Sheet: 1 of 1

Project Location: Park County, Montana

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Old Yellowstone Trail South, MT FLAP Park 2021(1)

E le va tio n (f t)

D ep th ft)

MATERIAL DESCRIPTION

TEST PIT LOG

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

L O

G

F H

W A

_D A

T A

T E

M P

LA

T

E .G

D T

/2 3/

:2

D :\O

Y T

S \O

Y T

S _2

_T E

S T

_P

IT

S .G

P J

Groundwater Depth:

Notes:

After Drilling: ---

While Drilling: --- At Completion: ---

Test pit located on north bound side of road.

Surface Elevation: 5087 ft Datum: MSL

Weather: Sunny

Date Started: 10/17/23 Date Completed: 10/17/23 Driller/Company: Cory Thornton/Park Cty Public Works

Logger/Company: Orion George/WFLHD

Equipment CAT 416E Approx. Excavation Dimensions: 2.5' x 7'

G ra ph ic

(7" = 100%)

(10" = 100%)

(10" = 100%)

(3" = 100%)

G01

M01

G02

G03

M02

Fines = 49% G02: R-value = 29 with density

78.1 pcf at moisture content 55.7%

Silty SAND with gravel, medium dense, dark brown, moist, fine sand to coarse sand, angular, clasts up to 3".

Rootlets within soil unit. ROAD SURFACING, infiltrated with subgrade.

0.8 ft / El. 5137.2 ft Silty SAND (SM), very dense, brown, moist, subrounded to rounded, ALLUVIAL DEPOSIT [AASHTO: A-6 (4)].

1.6 ft / El. 5136.4 ft Poorly graded SAND with gravel, loose, brown, moist, fine sand to medium sand, rounded to subrounded, with coarse sand and fine to coarse gravel up to 4 ".

ALLUVIAL DEPOSIT.

3.2 ft / El. 5134.8 ft Bottom of test pit at 3.2 ft.

D ril lin g

M et ho d

Field Blow Count (Recovery)No.

T yp e

Test Results

SAMPLE

SG23-07

Sheet: 1 of 1

Project Location: Park County, Montana

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Old Yellowstone Trail South, MT FLAP Park 2021(1)

E le va tio n (f t)

D ep th ft)

MATERIAL DESCRIPTION

TEST PIT LOG

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

L O

G

F H

W A

_D A

T A

T E

M P

LA

T

E .G

D T

/2 3/

:2

D :\O

Y T

S \O

Y T

S _2

_T E

S T

_P

IT

S .G

P J

Groundwater Depth:

Notes:

After Drilling: ---

While Drilling: --- At Completion: ---

Test pit on north bound side of road. Underground utilites located under south bound shoulder.

Surface Elevation: 5138 ft Datum: MSL

Weather: Sunny

Date Started: 10/18/23 Date Completed: 10/18/23 Driller/Company: Cory Thornton/Park Cty Public Works

Logger/Company: Orion George/WFLHD

Equipment CAT 416E Approx. Excavation Dimensions: 2.5' x 4'

G ra ph ic

(10" = 100%)

(6" = 100%)

M01

G01

G02

Fines = 45% G01: R-value = 19 with density of 95.9 pcf at moisture content 33.3%

Well graded SAND with silt and gravel, medium dense, light brown, moist, fine sand to coarse gravel, angular to subangular, ROAD SURFACING.

0.3 ft / El. 5310.7 ft Silty SAND with gravel (SM), medium dense, light brown with mottled yellowish tan and light gray, moist, fine sand, angular to subangular, with medium sand to coarse gravel, clasts up to 8". LANDSLIDE DEPOSIT [AASHTO:

A-7-6 (7)].

At 1.5': petrified log, ~ 16 inches circumference, encountered striking 031 deg az, highly fractured with fine sandy volcanic ash deposited around feature. Portion of log sampled by Park County for inculsion into County Historical Museum.

3.6 ft / El. 5307.4 ft Bottom of test pit at 3.6 ft.

D ril lin g

M et ho d

Field Blow Count (Recovery)No.

T yp e

Test Results

SAMPLE

SG23-08

Sheet: 1 of 1

Project Location: Park County, Montana

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Old Yellowstone Trail South, MT FLAP Park 2021(1)

E le va tio n (f t)

D ep th ft)

MATERIAL DESCRIPTION

TEST PIT LOG

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

L O

G

F H

W A

_D A

T A

T E

M P

LA

T

E .G

D T

/2 3/

:2

D :\O

Y T

S \O

Y T

S _2

_T E

S T

_P

IT

S .G

P J

Groundwater Depth:

Notes:

After Drilling: ---

While Drilling: --- At Completion: ---

Test pit on the north bound side of the road.

Surface Elevation: 5311 ft Datum: MSL

Weather: Sunny

Date Started: 10/18/23 Date Completed: 10/18/23 Driller/Company: Cory Thornton/Park Cty Public Works

Logger/Company: Orion George/WFLHD

Equipment CAT 416E Approx. Excavation Dimensions: 2.5' x 4'

G ra ph ic

(10" = 100%)

(3" = 100%)

(3" = 100%)

M01

G01

G02

M02

G03

Fines = 18% Moisture content 9.0%

Fines = 67% Moisture content 22.7%;

Organic content 2.1%

Fines = 49%

Silty SAND with gravel, medium dense, brown, moist, fine sand to medium sand, subangular to rounded, with coarse sand, and fine to coarse gravel, clasts up to 3" observed. ALLUVIUM mixed with ROAD SURFACING.

0.4 ft / El. 5052.6 ft Silty SAND with gravel (SM), medium dense, brown, moist, fine sand to medium sand, rounded to angular, with coarse sand, and fine to coarse gravel, cobbles up to 2.0' observed. Fining downward trend. ALLUVIAL

DEPOSIT [AASHTO: A-2-6 (0)].

1.6 ft / El. 5051.4 ft Silty SAND (ML), medium dense, dark brown with streaked black, moist, fine sand, pockets of fine sand observed. Roots within unit. ALLUVIAL DEPOSIT

[AASHTO: A-6 (7)].

3 ft / El. 5050 ft Silty SAND (SM), loose, brown, moist, fine sand, some fine to coarse gravel, ALLUVIAL DEPOSIT [AASHTO:

A-4 (0)].

6 ft / El. 5047 ft

Bottom of test pit at 6.1 ft.

D ril lin g

M et ho d

Field Blow Count (Recovery)No.

T yp e

Test Results

SAMPLE

SG23-09

Sheet: 1 of 1

Project Location: Park County, Montana

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Old Yellowstone Trail South, MT FLAP Park 2021(1)

E le va tio n (f t)

D ep th ft)

MATERIAL DESCRIPTION

TEST PIT LOG

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

L O

G

F H

W A

_D A

T A

T E

M P

LA

T

E .G

D T

/2 3/

:2

D :\O

Y T

S \O

Y T

S _2

_T E

S T

_P

IT

S .G

P J

Groundwater Depth:

Notes:

After Drilling: ---

While Drilling: --- At Completion: ---

Test pit in middle of the road. Connie Constan, USFS Archeaologist, on site during excavation.

Surface Elevation: 5053 ft Datum: MSL

Weather: Sunny

Date Started: 10/18/23 Date Completed: 10/18/23 Driller/Company: Cory Thornton/Park Cty Public Works

Logger/Company: Orion George/WFLHD

Equipment CAT 416E Approx. Excavation Dimensions: 2.5' x 8'

G ra ph ic

(3" = 100%)

(7" = 100%)

(7" = 100%)

G01

M01

M02

G02

G03

Fines = 61% Moisture content 16.7%

Fines = 19% Moisture content 9.5%

Silty SAND, medium dense, brown, moist, fine sand, RECENT FLOOD DEPOSIT (June 2022).

0.3 ft / El. 5050.7 ft Sandy SILT (ML), medium dense, dark brown, moist, fine sand, rounded, some medium to coarse sand, some fine to coarse gravel, clasts up to 5". ALLUVIAL DEPOSIT

[AASHTO: A-4 (0)].

2 ft / El. 5049 ft Silty SAND (SM), loose, brown, moist, fine sand to medium sand, rounded, ALLUVIAL DEPOSIT [AASHTO:

A-2-4 (0)].

4.7 ft / El. 5046.3 ft Poorly graded SAND with gravel, loose, brownish gray, moist, medium sand to coarse sand, rounded, with fine to coarse gravel, clasts up to 4", ALLUVIAL DEPOSIT.

5.3 ft / El. 5045.7 ft Bottom of test pit at 5.3 ft.

D ril lin g

M et ho d

Field Blow Count (Recovery)No.

T yp e

Test Results

SAMPLE

SG23-10

Sheet: 1 of 1

Project Location: Park County, Montana

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Old Yellowstone Trail South, MT FLAP Park 2021(1)

E le va tio n (f t)

D ep th ft)

MATERIAL DESCRIPTION

TEST PIT LOG

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

L O

G

F H

W A

_D A

T A

T E

M P

LA

T

E .G

D T

/2 3/

:2

D :\O

Y T

S \O

Y T

S _2

_T E

S T

_P

IT

S .G

P J

Groundwater Depth:

Notes:

After Drilling: ---

While Drilling: --- At Completion: ---

Test pit in north bound side of road. Operator reported 2022 flood deposited 5 feet depth of sand and silt on the site; most blew away since event.

Surface Elevation: 5051 ft Datum: MSL

Weather: Sunny

Date Started: 10/18/23 Date Completed: 10/18/23 Driller/Company: Cory Thornton/Park Cty Public Works

Logger/Company: Orion George/WFLHD

Equipment CAT 416E Approx. Excavation Dimensions: 3.5' x 8'

G ra ph ic

(4" = 100%)

M01

G01

G02

Fines = 78% Moisture content 4.9%

Poorly graded SAND with silt and gravel, medium dense, brown, moist, fine sand to medium sand, with coarse sand, and fine to coarse gravel, ROAD SURFACING.

0.2 ft / El. 5050.8 ft SILT with sand (ML), medium dense, brown, moist, with fine to medium sand, trace fine to coarse gravel, ALLUVIAL DEPOSIT [AASHTO: A-4 (0)].

4.7 ft / El. 5046.3 ft Poorly graded SAND, loose, brown, dry, medium sand, clean medium sand with roots growing into the unit.

ALLUVIAL DEPOSIT.

5.2 ft / El. 5045.8 ft Poorly graded SAND with gravel, loose, brown, dry to moist, fine sand to medium sand, with coarse sand, and fine to coarse gravel, ALLUVIAL DEPOSIT.

6.5 ft / El. 5044.5 ft Bottom of test pit at 6.5 ft.

D ril lin g

M et ho d

Field Blow Count…