Elder Creek, part of the South Fork Eel River watershed, lies in the Franciscan Formation found underfoot in most of the Northern Coast Ranges of California. The rocks here were deposited in marine environments when the Farallon slab was still subducting under the North American plate at this latitude. Subsequent uplift following the passage of the Mendocino Triple Junction has elevated these rocks out of the sea.
Clastic sedimentary rocks found in Elder Creek record information about their depositional setting. Grain size, lithology, and shape all provide clues about the energy of the flow and the time spent in transit, sorting and abrading. The vast majority of the rocks in Elder Creek are turbidites, formed from turbidity currents: dense slurries of sediment sloughing off the edge of the continent, rushing off the continental slope to final resting places in deeper, still waters. These currents are thought to be triggered by earthquakes, among other things.
Turbidites contain sand and pebbles that were rounded in terrestrial rivers prior to their arrival at the ocean. They also contain small clay-sized particles that fall out of the ocean water column (the long snowfall, in Rachel Carson’s words). As numerous currents are laid down over time, they create a rhythmic sequence of grain sizes, with a fining upward sequence recording stratigraphic ‘up’ (left to right in the image from the bed of Elder Creek below.)
Rhythmically bedded turbidite sequence (pebble to sand to clay size), Elder Creek. Photo credit: Jesse Hahm
Sometimes turbidity currents race over clay-sized mud deposits (shale). They pick up bits of the semi-lithified shale and carry them along. These shale bits are called rip-up clasts or intra-formational clasts. They are recognized by their darker color and angular shape, and are often much larger than the terrigenous sediment that surrounds them.
Rip-up (intra-formational) shale clasts in sandy matrix, Elder Creek. Photo credit: Jesse Hahm
Photo by Mary Power
doesn’t smell like scrambled eggs…
Oscar and the giant slime mold
Oscar Chang and I encountered this bright yellow spongy mass on a mossy rotten log on the south (left looking downstream) bank of Fox Creek, about 50 m up from the confluence with South Fork, in early June 2013, when we were helping Hiromi Uno install her mayfly-trout experiment. The vivid slime mold color got our attention! Slime molds, considered protists like ameoba even though they are societies rather than single celled organisms, deserve our attention. Some very clever Japanese scientists have made them seek food through mazes, and found out that foraging slime molds could eventually optimize traffic patterns through some major cities of the world—check out slime mold foraging here: http://www.scientificamerican.com/article/brainless-slime-molds.
July 2014 was perhaps the most intense yellow jacket season we’ve ever experienced at Angelo. On July 17, 2014, Casey Huckins and Mary Power spotted a “yellow jacket” in a funnel web’s spider web on the road cut banks along the east side of Wilderness Lodge Road, between Skunk Creek and Elder Creek.
On closer inspection, the insect turned out to be a beetle–it had hard wing covers (elytra). This mimic looked and moved very much like a yellow jacket, close enough to fool us, almost. The closest match I (Mary) could find was Typocerus zebra, Zebra longhorn beetle, Cerambycidae, subfamily Lepturinae. I’m not sure whether they’re native here or not; the species in the photos occur in Tennessee and Texas. Joyce Gross was interested in whether this genus is expanding into
northwestern California, or has been introduced. Next time you see a solitary yellow jacket, look for the split of the elytra down the back. If anyone knows more about this beetle, we’d be interested. If you see a bunch of yellow jackets, though, run! (or rather, walk away, quickly) as you may have disturbed a nest. Always smart to carry benadryl tablets (sold at Geigers in Laytonville), and an Epipen if you think you may be allergic~mep