A spectactular exposure of the detachment fault. The hanging wall is composed of syn-tectonic conglomerate composed of clasts derived from the footwall. The fault zone is composed of fine-grained gouge and overlies a thick section of pervasively deformed and altered crystalline rocks in the footwall.

Complexly-folded fault gouge (click for large image)

Brecciated rocks in the footwall (click for larger image)

Our first study area was the Sacramento Mountains, which were studied in detail by UWYO's own Erin Campbell-Stone. The day began with an examination of the crystalline basement rocks, which form the footwall of a large detachment fault. We then proceeded up-structure toward the hanging wall rocks, and finally to a spectacular exposure of the detachment fault itself.

Examining the footwall rocks - Sacram granite intruded by mafic dikes. Up the wash, we can see the intrusive contact of the granite with the (darker) Proterozoic gneiss, also in the footwall.