I’ll be giving a chat quickly out at Lafayette Reservoir, so I believed I’d pay the positioning a go to beforehand.
Strolling is at all times extra attention-grabbing than driving. From a automotive I’d by no means have seen East Bay MUD’s Mokelumne Aqueduct. As an alternative of a half-mile of roadside trudging, I had an attention-grabbing stroll alongside the right-of-way. Components of it are empty:
Components are absolutely civilized:
And elements are in between.
East Bay MUD developed the Mokelumne River water provide within the late Nineteen Twenties with all deliberate velocity, connecting Pardee Reservoir within the Sierra foothills to a really thirsty East Bay inhabitants. It was as essential to our well-being because the Hetch Hetchy system, being constructed on the similar time, was for San Francisco. The aqueduct is definitely three huge pipes of accelerating dimension, in-built 1927, 1949 and 1963, that run practically 100 miles throughout the Central Valley, dipping deep beneath floor to cross three rivers. They finish simply west of Lafayette at San Pablo Reservoir.
The aqueduct runs by central Lafayette simply south of the Route 24 freeway, and a close-up zoom in Google Maps reveals the land parcels it runs by. However my first inkling was once I set out from the BART station’s south car parking zone and noticed the indicators.
The aqueduct path begins on the prime of this slope, however higher to entry it from Dolores Drive a bit of west. That’s sufficient to say concerning the path for now; test it out a while. I’ve visited a number of main California aqueducts, and that matter deserves a separate publish.
Lafayette Reservoir is by far the smallest energetic water physique within the EBMUD system. Although it’s purposeful in case of emergency, the property’s major use has been leisure since 1966.
The lake has a negligible watershed, as seen within the digital elevation mannequin.
Its water degree is carefully regulated to maintain the vegetation, fish and boaters glad.
Humorous factor concerning the reservoir is that it’s solely about one-third the scale it was designed for. Let me quote from EBMUD’s magisterial historical past, Its Title Was M.U.D.: A Story of Water:
Sadly the most effective laid plans of even essentially the most diligent engineers can go awry. First there was unexpected issue with Lafayette Dam. Began in the summertime of 1927 and hindered by rains, it was solely eighty per cent full by September 1928 when work needed to cease abruptly. The earthen barrier was sliding on its foundations, opening nice cracks within the reservoir mattress. It continued for ten days, then stopped. A consulting board really useful that the dam base be widened and the ratio of peak to width lower by about half. This would cut back future storage within the reservoir from 10,540 acre toes to about 3,700, however by slicing the peak some forty toes and flattening the slopes they may at the least forestall an unpleasant blemish on the panorama. Work was delayed quickly and reconstruction prices ran to $300,000, however the misshapen dam has by no means moved since.
It’s so huge and low that it hardly even appears to be like like a dam — extra like a spot to throw an enormous live performance.
That historical past is why the tower within the reservoir is forty toes too tall. (They’ll shorten and strengthen it beginning in 2024.)
The rock across the reservoir, a nondescript mudstone, imposes a cloth on the panorama that’s seen in a digital elevation mannequin.
You’ll see the rock’s refined layering right here and there on the path. To map these rocks takes extra than simply them.
The 2000-vintage regional geologic map I often depend on paints this space as largely a poorly dated mudstone with little distinction. “Tus” stands for “unnamed Tertiary sandstone.”
Ross Wagner is a neighborhood geologist who’s spent many years poking across the East Bay hills, enlisting fossil consultants and students of volcanic ash to enhance his meticulous subject mapping. In his current interpretation of the rocks across the reservoir, he assigns most of it to the Orinda Formation (“Tou” for Higher Orinda Member of the Contra Costa Group).
From Wagner et al. in GSA Memoir 217 (2021)
The presence of the Rheem Tuff, the ash mattress from an historical eruption in a spot, as soon as close by, that now lies close to Santa Rosa, signifies an age of about 10 million years. The map appears to be like actually sophisticated, however the particulars are refined. The essential function is that the rocks on the south aspect are all tilted downward such that they get youthful as you progress south, and elsewhere the rocks are tilted the opposite approach, suggesting the presence of outdated inactive faults (the heavy traces) between these areas.
The tilted rocks are evident on the naked ridge on this view from Could 2022. The grass grows otherwise on the totally different rock layers, making them particularly seen throughout spring.
View west throughout the higher basin of the watershed from a degree south of the reservoir. On the horizon, naked Excelsior Peak is flanked by Frowning Ridge and Vollmer Peak on left and proper.
The East Bay has been very busy for a great 12 million years. When these rocks had been being laid down the panorama in all probability resembled elements of Indonesia. The panorama we all know at this time, together with Mount Diablo, has taken form solely within the final couple million years.
Get pleasure from it at this time.
