Taken from the TROUTDALE, VA, 1:24,000 quadrangle, 1959, rev. 1978
Directions: park on the west-bound side. There is a slightly wider patch of gravel shoulder that can hold 4 vehicles. The roadcut is on the opposite side from the gravel shoulder. Be careful of the traffic. The photo below shows the spot facing westbound. Note that the vehicle parked on the right for scale isn't a little car...it's a full-sized Chevrolet Suburban.
Be careful as you cross the road to get a closer look at the outcrop. What seems like a quiet country road is actually a main route to the Mount Rogers area. The "locals" tend to drive this road fast, so keep a close watch! Once you are safely standing close to the outcrop, take both closeup views and views from a few feet back. Then answer the questions below.
Geology preview: this is an excellent introduction to the rock types of the Mount Rogers Formation. The Mount Rogers is a diverse formation containing igneous and sedimentary rocks. This outcrop is of the lower part of the Mount Rogers Formation and is a type of rock called "conglomerate" - a rock composed of gravel and cobbles of other rocks. All the different types of rocks that can be found in the lower Mount Rogers (and rocks that are older) are represented in the cobbles. We will see many of these rocks again later in the trip. General age of the rock here is approximately 760 million years old - the "late Proterozoic".
Answer the questions below. Then, check your answers by clicking the "Answer" link. No cheating, now! This is an open-slope test!!
QUESTION 1:
Notice that the outcrop is composed of a number of different rock types. The larger rocks, or cobbles, are of different types, shapes and colors. The photos below cover some of the main types of rock. Identify the 5 main rock types that compose the cobbles. An important point to note here is that the rocks preserve two aspects of their history: the history surrounding the origin of each of the 5 main rock types, and their later history as cobbles within this sedimentary rock! Answer
White, hard, translucent pure quartz.
Quartz-rich, feels rough, composed of rounded sand grains.
Pink feldspar, with quartz, coarse grained, faint green "micaceous" bands.
Left: fine grained, dark greenish gray.
Maroon, fine grained with prominent coarse feldspar grains with good crystal faces.

QUESTION 2:
Look at the size and shape of the cobbles. Note that the cobbles touch each other (we say that they are "grain supported"). Under what conditions might a rock like this form? (Hint: turn around and look at what is on the other side of the road.) Answer
QUESTION 3:
Taking everything that we have observed at this outcrop into account, what might this imply about the type of topography that existed in this place during the late Proterozoic? Answer
Link to Stop 2
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