Latitude 33.18 N, longitude 116.769 W, elevation 3,238’.
This here hasn’t always been here. I want someone to sit with me and tell me how these landforms were made: those peaks, this humpy upland, the pile of rocks below the house.
deep time
orogeny, mountain building
plate-margin encounters, slidepast plate contact
basement or country rock, native to an area
Coming ignorant into geology there are so many foreign words, many of them charming, some of them numbingly technical,
What little do I know so far.
Peninsular Ranges 80 miles east of the coast
Broad upland plateaus.
The topography is varied in the Santa Ysabel-Julian area, ranging from less than 1000 feet to 6,533 feet above sea level. The rock unit on which the Santa Ysabel-Julian area is situated is part of the Southern California Batholith, a mountain belt extending from Los Angeles County to the tip of Baja California. About 10% to 15% of the landscape in the Santa Ysabel-Volcan Mountain Preserve features exposed rocks. Most of the rocks that one sees when driving through the Santa Ysabel-Julian area have one of two origins: rocks that have risen from several miles beneath the surface of the earth where they were formed over one hundred million years ago; or rocks that were created over two hundred million years ago when ancient sea floor sediment was metamorphosed through heat and pressure.
molten emplacement of peninsular batholith from beneath … limestones were metamorphosed into marble, sandstones into quartzite, and sandy shales into schist and gneiss
Eastern half of the Range “ancient sedimentary country rock folded, metamorphosed and intruded by granitic/plutonic magmas” – the Peninsular Ranges batholith. Western half “an island arc formed 1000 miles to the south,” creeping north 50 millimeters a year. Faults where they meet, San Andreas and others, valleys running approximately along the faults.
Along the eastern edge of the Peninsular Range, intermittent appearances of much older rock, a “thin spine of primeval metasedimentary strata dating to about five hundred million years ago.”
On roadside cutbanks I’ll sometimes see the sort of white vein that is a “late intrusion” and may bear tourmaline or gold.
The nearest fault, slow-creeping Elsinore at .15” a year, lies maybe 6 miles away, almost under Highway 79 where I turn off Mesa Grande Rd on the way to Santa Ysabel. When I learned that I started parking farther from large trees.
