I am a snow snob...I admit it. This winter has seen less-than-great ski conditions and so when the temperatures in Southern Arizona were in the mid 70 degree range we thought a visit was in order.
Our major objective was to enjoy the warmth, ogle the Saguaro cactus and hike as much as possible while wandering the hillsides above Tucson we started to notice the abundance and great examples of crystalline rock, both igneous and metamorphic rock. The outcrops we examined were not anything we were familiar with beyond a very general way. The granites appeared to have been drastically changed and the gneisses looked like they had been put through the wringer.
The mountains we were hiking in were formed in mid-Laramide time when a large detachment fault allowed a decidedly large rock mass to slide while the Catalina Mountain were arching upwards. The material that moved along the fault was metamorphosed considerably, giving us some awesome outcrops to examine. Since then, erosion and weathering has moved materials from the mountain tops into the broad valleys. Many of the hiking trails use these alluvial fans to gain access to the higher elevations. Garry at geotripper has also just recently written about these mountains
Hiking in the Catalina Mountains with examples of granite that had not been altered during the formation of the Catalina Mountains.
Further out from the mountains we came across this outcrop of mylonitic gneiss, a former granite that was abused by its passage along a detachment fault as the Catalina mountains were being uplifted 25ish million years ago.
A fun outcrop of gneiss, another remnant of movement of granite along the fault.
You can never be too careful riding your bike around interesting geology.
A trail crew with an eye for aesthetics and geology. An assortment of metamorphic rocks making a wall.
Hiking across an alluvial fan; Saguaro and geology at the same time.
