Type Formation | Country United States | |
Region San Diego County, California | ||
The Poway Formation is a geologic formation in San Diego County, Southern California. It preserves fossils dating back to the Paleogene period.
Poway clasts
Volcanic clastic rock cobbles of rhyolite, in a sandstone matrix in this area are named Poway clasts.
The ancient Ballena River brought rhyolite-gravel, or “Poway" clasts, from a region in present-day Sonora, Mexico to the Pacific Ocean. Its sediments deposited into alluvial fan-submarine canyon-submarine fan complex extending for miles offshore. Remnants of submarine fan facies outcrops are found as far west as the northern Channel Islands. Inland Ballena River deposits outcrop discontinuously over 16 miles (26 km) in a west-southwest trend from Whale Mountain to San Vicente Reservoir, here the river was up to 2 miles (3.2 km) in width through Peninsular Ranges.