Category Archives: Los Angeles County

Mt Wilson Observatory Geology Talk

Lectures

On Saturday, June 16, at 5:30 pm Mount Wilson Observatory will be hosting a talk by Dr. Tanya Atwater, professor emeritus of geology at UC Santa Barbara. Dr. Atwater played a major role in piecing together the plate tectonic history of our part of the planet. She will talk about how the motions of the Earth’s crust created the current topography of southern California (including the perfect site for astronomers to explore the Universe). The talk will be followed by a rare chance to look look through Mount Wilson Observatory’s 60-inch Telescope, which revolutionized telescope design and allowed astronomer Harlow Shapley to find our place in the Milky Way Galaxy. Tickets are only $20 and proceeds will all go to the maintain the Observatory.

Featured Image – March 12 and 13, 2018

Photo of the St. Francis Dam just before it collapsed.
Side view of the dam. Note the lack of any real spillways in the dam. Water was about one foot below the rim of the dam the day of the collapse.

This featured image covers two dates for a reason. The St. Francis Dam, a former dam in San Francisquito Canyon above Santa Clarita, California, collapsed at 11:57:30 pm on March 12, 1928. The ensuing flood caused a great deal of damage along the canyon and the Santa Clara River Valley. Over 500 lives were lost that night in, even in 2018, the second largest disaster by loss of life in California. The even had repercussions throughout the world. Following that event, dams, as well as other large projects, no longer were approved by engineers. Geologists had the final say, not engineers. Both geologists and engineers also had to be certified by their state government to work as professionals.

The head engineer on the project, William Mulholland, was a great engineer. He oversaw and helped design the Los Angeles Aqueduct, which was the largest and longest project of its time. It is still an engineering marvel today, more than 100 years later. The disaster ruined his career and during the investigation, he not only took full responsibility for the event, but also was said to have “envied the dead”. The collapse took a big toll on the “Chief” and he died a few years later.

This post is in memory of both those that died that fateful night in 1928 and to William Mulholland. A man that went from the “Savior of the City” to a pariah in just a few years.

Image of the Week – 8/27/2017

Looking toward Timber Mountain with Mt San Antonio and Cattle Canyon to the left.

US 6 – Santa Clara River Bridge – A Closer Look

US Highway 6, now known as Sierra Highway, crossed the Santa Clara River near Solemint, California. The bridge it originally used, constructed in 1938, is planned to be replaced in the near future. This bridge is one of the oldest remaining in the Santa Clarita area and is the longest span on former US 6 in California. The bridge has remained almost intact from its original construction. The only changes have been minor to the bridge itself. The highway, however, has changed quite a bit. In 1968, Sierra Highway, then State Route 14, was widened to four lanes. A second bridge for northbound traffic was added, with the original bridge being used for southbound traffic.

Presently, Sierra Highway is six lanes wide at the river crossing. As the bridges were built with a four-lane highway in mind, only a narrow shoulder along both directions exists. This condition is one of the reasons the bridges across the Santa Clara River are being replaced.

In March of 2017, I took a trip to inspect in more detail the bridge and the surrounding area. It was nice to see the bridge again, as it brought back a lot of memories. I used to live near the bridge and crossed it almost daily. It will be sad to see it go as it is one of the last remaining pieces of the old highway. So, please, check it out yourself while you still can. I’m not quite sure when the construction will begin, it may have already.

Main Structure:

Side view, from the northern end. Note the small arches along each span.
Southern abutment and wing wall.
Between the 1938 and 1968 spans. Quite a difference between the girders.
Deck view, looking northerly from the south end.
Side view showing the railing, arched spans, and wing wall.

Detailing:

Underside view of the bridge.
Closeup of the west side railing from the south end of the bridge.
View showing the railing at the expansion joint.
Expansion joint that may have moved during an earthquake or from settling.
Expansion joint along the bridge deck.
Deck drain detail.
Remaining section of railroad rail and wire fence embankment protection.

Los Angeles County Survey Records

Los Angeles County Department of Public Works has a wealth of information available on their website. With a bit of patience and some looking around, you can find quite a few treasures using their mapping application. I’ve so far found the original survey data for the “Bridge To Nowhere” roadway, plans for other roadways that were never built in the Sierra Pelona Mountains, as well as the forest service permit for the Shoemaker Canyon Road that was never completed.

http://dpw.lacounty.gov/sur/landrecords/index.cfm