I mapped this unit back in 1976-77, and collected this rock in the Rincon Mountains. My most unusual experience along this contact was in the Catalinas. While I was sitting on the outcrop of ultramylonite writing copious notes, I became aware of two hikers, a man and a woman, on the ridge opposite. They were talking away, but suddenly fell silent, and when I looked up I realized that they decided to make love right on the spot. That’s the ‘70s for you. Funny, I felt like the intruder from 40 m away, and never looked up once after I realized what was happening. This is more than you thought you would learn about ultramylonite in the Catalina Rincon metamorphic core complex. Just checking to see if anyone is reading all of this stuff.
Age & Formation
The ultramylonite formed in the Miocene, ~25 to 18 Ma. The protolith from which it was derived was a combination of Mesoproterozoic quartz monzonite (~1.42 Ga) and Eocene two-mica garnet bearing granite (~55 Ma).