Stop #4 Quartzite Wall
Closely examine any of the large quartzite boulders which have fallen from the walls. These boulders were once a part of the sheer faced walls above. Due to the physical properties of water, these large boulders have become dislodged and have tumbled down to the trail. This happens when water enters a small crevasse in the rock and then freezes when temperatures allow it to. When water becomes solid it expands, this slowly opens the crevasse. This water melts and allows more water to enter the crevasse. When this cycle of freezing and thawing continues, primarily in the late spring or early fall, the crevasse enlarges and the rock becomes unstable. This is known as frost wedging. Another minor contributing factor are plants. When a plant establishes itself in a crevasse, the roots of the plant can cause the crevasse to expand, as was the case with frost wedging. This process is known as root wedging.
At first glance, the rock appears to be a well sorted quartzite (Sorting refers to the variation in grain size). However, upon a closer look, the quartzite boulders contain a number of small cobbles and pebbles. Outside of these small cobbles, the rock is composed entirely of small well rounded quartz grains. These observations, along with a few more further up the trail, allow geologists to predict what this area looked like during the time of deposition. The fact that the quartzite is composed almost entirely of well rounded quartz grains is indicative of a beach environment. Imagine what the beach looked like the last time you visited. The beach must have been very close to a topographical highpoint due to the size of the small cobbles. Cobbles of that size do not get carried very far from their source.
Picture a beach with a nice breeze blowing and a series of hills rising behind you. That is what this area must have looked like many years in the past. By examining the clues left in the rocks that you see, you can begin to interpret the environment at the time of deposition. This type of observation and prediction, allows geologists to make important economic decisions.
Look to the north side of the canyon. You should be able to see a small mine that has been drilled into the quartzite. Directly to the east of this mine, the layers of quartzite begin to look contorted. Earlier observations made note that the bedrock was layered nearly horizontal, however, all that has changed. The quartzite has been folded into a vertical position, in some places it has been slightly overturned. If you will recall, Phase II of Rock Canyon’s geologic history was a period of immense change in the canyon. The west coast of North America was colliding with numerous tectonic plates moving from the west. These folds are the evidence for this event.
These contorted layers were essentially pushed up along a shallowly sloped ramp. As the rocks moved over the ramp, they were crumpled and folded. This type of folding continues the remainder of the way up the canyon, however, is not as easily seen as in this portion of the canyon.
Just to the west of the Old Mine you will note two interesting observations. First, follow the Mineral Fork Tillite (olive-brown layer) from the west to the east. The layer disappears just to the southwest of the mine. This layer has been folded as well, and does not stop abruptly as it appears, it continues down below what is visible.
Next, look at the sudden jump in elevation of the tillite just to the west of the mine. It appears as if a block of this layer was pushed above the neighboring sections. In effect, that is exactly what has happened. Imagine sliding on a carpet, the carpet responds by creating upthrown portions in the middle area of the carpet. As this layer was being pushed from the west by continental collision, it was also being pushed from the east by the overturned layers. This portion of the tillite responded to the compressional forces by faulting, and was thrust skyward. . This process is known as reverse faulting.
Continue up the canyon until you have reached the gate. The vertical layers to the south are still the Tintic Quartzite. The trail will continue through the Tintic Quartzite for approximately 1000 feet. This is also the thickness of this formation (see geologic map). Since these beds are tilted vertically, you are walking the entire depth of the quartzite, starting from the oldest layers and continuing to the youngest. The area surrounding the gate is used by beginning rock climbers. The climb is not too severe, yet it is a great outcrop to learn on.