May Speaker: “Actinolite, Alpine Mudflows, and the San Andreas Fault” by Debra Brooks

by Cindy Schmidtlein, MSDC Vice President

Actinolite from Wrightwood, CA. Photo by Debra Brooks.

Our speaker for May is Debra Brooks, a Geology Professor Emerita at Santiago Canyon College in Orange, CA. She will talk to us about actinolite, a green, amphibole mineral that commonly occurs in greenschists formed by the regional metamorphism of mafic rocks in relatively low-temperature and medium-pressure environments. Actinolite can vary in habit from asbestiform to compact, or as crystals with a vitreous luster, bladed habit, splintery fracture, growing in radiating masses, which describes the actinolite found at Wrightwood, CA, the focus of her talk.

Not Your Typical Resort Town

Located in the San Gabriel Mountains of Los Angeles and San Bernardino Counties, Wrightwood is a small ski resort town with proximity to outdoor recreational areas for picnicking, camping, hiking, and backpacking in the surrounding Angeles National Forest. The Pacific Crest Trail runs along the crest of the Blue Ridge of the San Gabriel Mountains and includes Wright Mountain at the southern edge of town.

The town also sites directly on the San Andreas fault and below the Wright Mountain landslide, both of which contribute to its annual debris flows and mudslides, locally known as “Alpine Mudflows.” In 1941, the mudflows virtually destroyed the town.  It exists today only because the U.S. Army Corps of Engineers built diversion channels for the debris/mud flows.

Debra’s Background as Geophysicist and Professor

After graduating from UC Riverside in 1978 with a BS in Geophysics, Debra was employed by Amex, Inc. as a field geophysicist in mining and geothermal exploration in the western U.S. She later went back to college as a graduate student at Texas A&M and eventually completed an MS in geophysics while working in petroleum exploration as a senior exploration geophysicist for Exxon. In the early 90s, Debra chose to stay in California rather than move to Texas for her job and took a position as adjunct faculty at Chaffey College, Victor Valley College, and CSU San Bernardino.

In 1993, she got a full-time, tenure-track position at Santiago Canyon College (SCC). She retired from SCC in 2020 as a full professor and department chair after 27 years of teaching geology. While retirement is fun, she missed teaching, so in 2023 she returned to SCC as adjunct faculty. She is also part of a group of community college and Cal State geology professors who are currently writing a textbook on the geology of California with the support of a grant from the Chancellor’s Office of the California Community College System.

Debra’s talk will include personal tales of how I became aware of Wrightwood as a collecting site for actinolite, and the joys of including it as a stop on community college geology fieldtrips.