The Murrieta Hogbacks are

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

capped granitic hogbacks located in northeastern

Murrieta Murrieta is a city in southwestern Riverside County, California, United States. The population of Murrieta was 110,949 as of the 2020 United States Census, 2020 census. Murrieta experienced a 133.7% population increase between 2000 and 2010, ma ...

on the southern end of the

Temescal Mountains Temescal Mountains, also known as the Sierra Temescal (Spanish for " sweat lodge range"), are one of the northernmost mountain ranges of the Peninsular Ranges in western Riverside County, in Southern California in the United States. They extend ...

Riverside County, California Riverside County is a County (United States), county located in the southern California, southern portion of the U.S. state of California. As of the 2020 United States Census, 2020 census, the population was 2,418,185, making it the fourth-most ...

Geology

The Murrieta Hogbacks are underlain by

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

granitic rocks of the Peninsular Ranges Batholith. On the north half of the hogbacks, by foliated

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more alumino ...

- hornblende tonalite and on the southern half by hornblende

gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is che ...

. The basalt is potassium-argon dated to 10.4 to 10.8 million years and is a remnant of a channel-filling basalt flow, overlying a thin deposit of unconsolidated gray stream gravel, indicating that the basalt had filled in a former water course.M.P. Kennedy and D.M. Morton, PRELIMINARY GEOLOGIC MAP OF THE U.S. Geological Survey Murrieta 7.5' quadrangle, 1979, RIVERSIDE COUNTY, CALIFORNIA, Version 1.0, USGS, Prepared in cooperation with the CALIFORNIA GEOLOGICAL SURVEY, 2003.

References

Mountains of Riverside County, California Temescal Mountains Mountains of Southern California {{RiversideCountyCA-geo-stub