* On the east side: The Uncompahgre Fault Zone. This is a major, northwest-trending fault zone that extends for over 100 miles. It is a reverse fault, meaning that the hanging wall (the block above the fault) has moved upwards relative to the footwall (the block below the fault). This type of faulting is associated with compressional forces.
* On the west side: The La Plata Mountains Fault Zone. This is another major fault zone, also trending northwest. Like the Uncompahgre Fault, it is a reverse fault, indicating that the hanging wall block has moved upwards relative to the footwall block.
These two faults, both reverse faults, have played a significant role in shaping the Animas Valley, creating the distinct topographic features of the valley and the surrounding mountains. The uplift along these faults created the La Plata Mountains to the west and the San Juan Mountains to the east.
It is important to note that these faults are ancient and have been active for millions of years. While they are not currently experiencing large earthquakes, they are still considered active and capable of producing earthquakes in the future.
