The recent post of sand lines in the waters of Lake Tahoe (see: Tahoma (CA), Rock, Sand Lines, Underwater) reminds me of this photograph taken on Manchester State Beach in Mendocino County, just north of Point Arena, last year. While there is always the “purpose” of enjoying the sights and sounds of the waves rolling in and finding interesting rocks while beachcombing, the true unrealized purpose was to visit the exact location (gps: 39.004786, -123.695898) of the most northern point the San Andreas Fault enters into the Pacific Ocean.
Unfortunately the not quite two-lane county Alder Creek Beach Road that leads to the site is no longer open for vehicular traffic due to parts of road falling down to a creek below. So one of the alternatives is to park at Manchester and walk the length of the beach, which turns out to be more than couple of miles. Maybe by itself a two mile hike each way is not bad, but it is much worse in soft sand. We never made it, and ended up checking out the sand and surf for a couple of hours before touring the Point Arena Lighthouse.
Geology Notes: While the thought of where a major earthquake fault entering the ocean conjures up fantastic images of a big crack in the earth running into the ocean, that is not the case here. In reality it is just where Alder Creek meets the beach and enters the ocean. The only real evidence is only seen with a trained eye that can interpret the type, color, and striation of rocks that line the hills carved out by the creek. There are other minute changes on either side of the fault with reported observations describing difference in plant life, soil type, and even the compactness of the soil when walked upon.
Sites or book references about the San Andreas Fault in this area are:
- The California Earthquake of April 18, 1906: Report of the State Earthquake (pg 59-61, with photos)
- The Northern San Andreas Fault (images)
EXIF data: Nikon D7000, center-weighted metering mode, ISO100, 26mm, f/8, 1/160 sec
Manchester (CA), Sand Ripples, Monochrome. Manchester State Beach, Manchester, CA. June 29, 2015. © Copyright Steven Tze – all rights reserved.