4. Detachment Faults and the San Pedro Valley
[In the following discussion, you may want to refer to an authoritative geological time scale; to see one adapted from the work of the University of California Berkeley Museum of Paleontology (cited in Credits & Bibliography) click here.]
In Hot Springs Canyon, the Soza Mesa Fault (see Geology Trip up Hot Springs Canyon, under the heading "Soza Mesa Fault and the Willow Canyon Formation") appears to be the major detachment fault we can see. This fault is part of a regional process that began some 25 MYa and proceeded rather rapidly, along the lines of the diagram below:
In this diagram, West is on the right. The initial major detachment fault, which occurred somewhere in our area, began to form prior to the uplift of the Core Complex "pimple", generating a series of breakaway faults. As the Santa-Catalina mountain complex rose, the San Pedro Valley part of the fault became cut off ("fossilized"), then formed another set of lesser detachments. One of these detachment faults is the Soza Mesa Fault. The bottom diagram (taken from a publication by Jon Spencer and Steve Reynolds, adapted by Mick Meader to our area) shows the outcome of the process. Mick provided us with another diagram showing the process in three dimensions:
As the older rocks slid off the top of the Catalina-Rincon complex, this removed the overburden and allowed the hot underlying pluton to rise even higher.
Mick Meader provides the following map showing the position of the Soza Mesa Fault in relation to the Teran Wash Fault in Hot Springs Canyon:
For a summary placing the Mid-Tertiary Orogeny in its wider historical context, see Meader: Geological History of our Area.