Oh the Things We Do For Love...Thursday's Fun Foto Explained

Thursday's Fun Foto was taken during my brief Veteran's Day exploration of the Sierra Nevada foothills along Merced Falls Road. The area near the road is a deeply eroded and weathered landscape of metamorphic slate and greenstone dating to Jurassic time. The soils support grass and the occasional oak tree, and is an excellent environment for the star of our fun foto, the California Tarantula. We must have some arachnophiles out there because the guesses zeroed in on spiders. Our Sierra foothills are prime habitat for these huge arachnids.

The females spend most of their time in burrows waiting to ambush their prey, which consists mostly of crickets. They can live as long as 20 years. The males have it a bit tougher...their hormones, or whatever, cause them to emerge in September and October to seek mates. They are exposed to plenty of danger at this time, including the tarantula wasp, which likes to inject venom into the poor spider, paralyzing it, and making it into a food source for the egg the wasp lays in it. If the male finds a willing mate, he also has to keep from becoming a meal for the female if times have been lean. All in all, the males are lucky to live more than a few years.

As frightening and terrifying as they might appear, tarantulas rarely try to bite people, and even if they do, their venom is so weak that most people feel nothing worse than a bee sting. They are generally docile and would rather retreat from confrontation. They are also rather delicate; one source I ran across mentions that a fall of six inches can injure them while a fall of twice the distance can kill them.

One other sight during the afternoon was an interesting convergence of a number of road signs. Not really very geological, like those at Andrew Alden's site, but kinda funny. I expected to see the Roadrunner pass by with Wily E. Coyote in hot pursuit...

What a Difference a Week Makes: Fall Report from the Sierra Nevada Foothills

What a difference a week makes! Ten days ago we headed into the foothills looking for some fall colors and didn't see much, so I shot lichens instead. Last Saturday, I took students to Yosemite Valley, and there was merely a touch of color high on the cliffs. But we had a bit of a cold snap during the week, and it, uh, made a slight difference. We made a spur-of-the-moment journey to Yosemite Valley via the "John Muir Highway" and found a transformed landscape.

Aspens are the legendary fall color maker in many parts of the Sierra Nevada, but there are few aspens in the foothills and mid-elevation slopes of the western side of the Sierra. Instead there are many varieties of oak, sycamore and maple or birch (whose specific identities escape this biologically ignorant geologist).

Also missing from the scene are outcrops of granite. In the foothills north of Mariposa, most of the bedrock is composed primarily of metamorphic rocks of the Foothills Terrane, the Calaveras Complex, or the Shoofly Complex. These are Paleozoic and Mesozoic slates, quartzites, marbles, and greenstones that formed out in the Pacific Ocean hundreds or thousands of miles away, and which were accreted to the edge of the continent as the ocean floor was subducted beneath the North American continent.

Glaciers did not reach the mid- and lower level slopes of the Sierra Nevada, so soils are thick and deeply weathered, most often to a bright red color from the iron oxide content of the original minerals. The soils are not particularly rich for agricultural purposes, having been leached of the most important nutrients by high rainfall amounts and the relatively warm climate. The trees do just fine, though. As a consequence, logging has been an important part of the economy here in the past.

Highway 132 winds its way through Modesto to LaGrange, and then Coulterville. There is a long ignored alternative route to Yosemite that goes from Coulterville to Smith Station on Highway 120 which has garnered a bit more attention lately, having been designated as the "John Muir Highway" by local communities. I'm not sure how Muir would have felt having a road named after him, but it is a nice way to go. It's a bit winding and slower going, but provides some very nice views of some large meadows in the vicinity of Greeley Hill, and a panorama of the Clark Range in Yosemite National Park (above).

Once we were back on Highway 120, we stopped by Rainbow Pool, a popular swimming hole in summer. There is a deep pool and a short waterfall, along with some developments (parking lot, stairs and bathrooms) that make for easy access. There was no one there yesterday, just a beautiful stretch of river, and colorful foliage.