At ground zero you will observe the actions of a thrust fault. This thrust fault is named the Piney Creek thrust fault. Piney Creek thrust fault has carried a wedge-shaped block of Precambrian and younger sedimentary formations to their present position, some 2.5 miles east of the normal position of the mountain front. Stratigraphic displacement is estimated at 10,000 feet.
What is a thrust fault? A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger. Due to the movement of the thrust fault unearthing the lower layers, this basement rock from the Pre-cambrian era has been exposed.
At this location exposed lies Precambrian granite gneiss. The Piney Creek thrust fault shoved this portion of the central Bighorns over the western margin of the steeply inclined Paleozoic limestone and dolomite beds. The Piney Creek thrust, then cut into much older Precambrian basement rocks. The Precambrian basement rock that has been exposed is composed of extremely ancient metamorphic gneiss that are over 3 billion years old. This basement rock is primarily composed of granitic gneiss.
What is gneiss? Gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than other metamorphic rocks. In this case it is formed by the metamorphosis of granite. Gneiss, will display distinct foliation. Foliation in geology refers to repetitive layering in metamorphic rocks. These layers can vary in direction depending on the action, the forces and/or presence of a fault in the area. Each layer may be as thin as a sheet of paper, or over a meter in thickness. The word comes from the Latin folium, meaning "leaf", and refers to the sheet-like planar structure.
With the age of the Earth at 4.54 billion years old, the exposure at this section is unique and gives us a look at 3 billion year old basement rock. Without the presence of the thrust fault and road cut this exposure could not occur and be observed. 
To log this earth cache please answer or do the following:
1. How old is the Pre-Cambrian gneiss estimated at, at this location?
2. Observe the exposed gneiss at ground zero, how would you describe the foliation?
3. Look at the cross sectional image above. What is the name of the ERA of sedimentary rock that most closely borders the Precambrian crystalline rocks
4. Not required, but fun, please post a picture of yourself at the road side sign, but not of the exposed basement rock or your log will be deleted.
If answers are not sent within 7 days, logs will be deleted.
Sources:
1. Environmental Setting of the Yellowstone River Basin, Montana, North Dakota, and Wyoming AUTHORS: Ronald B. Zelt, Greg Boughton, Kirk A. Miller, Jon P. Mason, and Laura M. Gianakos
2. Structural Geology of the Piney Creek Thrust Area, Bighorn Mountains, Wyoming Author: ROBERT FRANK HUDSON
3. New interpretations of the Piney Creek thrust and associated Granite Ridge tear fault, northeastern Bighorn Mountains, Wyoming Rocky Mountain Geology, October 1, 2003, v. 38, no. 2, p. 205-235
4. Road Side Geology of Wyoming Author: David R. Lageson
5. WWW.WSGS.WYO.GOV