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Geologic Mapping

3rd Oct 2021 in

When my daughter Kelsey, (she now goes by her middle name, Grace, after my grandmother Grace Bartlett Kissam Duryee), was in 5th grade I was homeschooling her. For a science class assignment, I took her and two of her friends to the Elsinore Fault just east of Lake Henshaw in eastern San Diego County. The map below shows where we were.

San Diego County map
Map of northern San Diego County

We went to a road cut that I had been looking at for about a decade. Every time I drove by I pulled over and checked it out. I was fascinated by the spectacular fault exposure the roadcut displayed. I poured over geologic maps and publications learning all I could about that particular stretch of the Elsinore Fault. When I was growing up, my dad took me fishing at Lake Henshaw a number of times. He didn't know anything about geology, but the place seeped into who I am and I love the area to this day.

Satellite view of our mapping location

It was fun to share the place with my daughter and her friends, and they seemed to enjoy the project as well. Here's a satellite view of the region showing Lake Henshaw and giving a really good view of the Elsinore Fault. (The Elsinore is the southernmost division of the San Andreas Fault's "trilateral split". The San Andreas Fault Zone in Southern California is made up of the Elsinore, San Jacinto, and San Andreas Faults. At the point where we mapped the road cut, the San Andreas Trilateral Split Zone is about 50 miles wide.)

Geo Map Elsinore Fault
Geologic Map of the Elsinore Fault

Above is a geologic map showing the fault at the location we mapped. You can see the small fault branch we mapped that crosses Hwy 79 just north of the intersection with Hwy 76 labeled "Our mapping location".

And here are Kelsey, Amy, and Eric all working on making a geologic map:

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