Final answer:
The geological feature one would expect to witness in a cross-section of Mt. San Antonio within the Transverse Ranges is fault lines, which are indicative of the tectonic processes that have shaped this mountain range through the motion of the Earth's crust and tectonic plates.
Step-by-step explanation:
When viewing a cross-section of Mt. San Antonio, part of the Transverse Ranges, one would expect to witness geological features indicative of the mountain range's formation processes. The Transverse Ranges are characterized by strong tectonic activity influenced by the movement of the Earth's crust. Specifically, fault lines are the prominent geological feature associated with this region. They are the result of the forces that have shaped these mountains through the motion of tectonic plates over time.
The formation of the Transverse Ranges, including Mt. San Antonio, involves the interaction of the Pacific Plate and the North American Plate. This interaction has given rise to a series of faults, with the San Andreas Fault being the most well-known. These fault lines represent the lines of weakness in the Earth's crust where the plates have moved past each other, contributing to earthquakes and shaping the landscape.
So, when looking at a cross-section of such a mountain range, one would not typically expect to find volcanic vents, sinkholes, or karst topography, which are characteristic of different geologic settings and processes. Instead, the evidence of past and present tectonic activity in the form of faults is the expected feature.