Standing on Cretaceous granite in the hanging wall looking across the river at Paleoproterozoic gneiss in the footwall (click for larger image).

Banded, red-brown, cohesive fault gouge separates the granitic hanging wall and gneissic (green) footwall. This exposure is located on the east side of the river.

Miocene Peach Springs Tuff in the hanging wall on the east side of the river (click for larger image).

The Colorado River though the Needles/Topock Gorge area roughly follows the trace of the Chemehuevi detachment fault. Since the area is designated as a wilderness area and vehicle traffic is prohibited, the best (and most fun) way to access the area is by canoe.

In this panorama, the Chemehuevi mountains are on the right and the Needle mountains are on the left. The rocks of the Chemehuevi mountains are composed of Paleoproterozoic gneiss (right) and Cretaceous granitic rocks. They form the footwall for the Chemehuevi detachment fault and their slope generally preserves the dip of the fault. The Needles are composed of Tertiary volcanic and volcaniclastic rocks as well as megabreccia. They form the hanging wall of the detachment fault. The Colorado River in the foreground bends to the right and roughly follows the detachment.