It is a quick weblog sequence of informational articles from my school school web site that’s quickly to be extinct (arcane unsafe software program, they are saying). Manner again in 2002, the mum or dad of considered one of my college students provided me a flight of my selecting, and I knew it needed to be Stanislaus Desk Mountain. It is without doubt one of the extra well-known geological options of our area, and it’s best appreciated from above. Please buckle your seatbelts, and adjust to the no smoking indicators…

Our flight takes us from Oakdale, a small city on the foot of the Sierra Nevada, to the Sonora-Columbia space within the Sierra Mom Lode. Our goal was to get a chicken’s-eye view of the Stanislaus Desk Mountain, regarded by many as one of many most interesting examples of an inverted stream on the planet. The “mountain” shaped round 9 million years in the past, when a latite lava circulation streamed westward from vents within the neighborhood of the Dardanelles, close to Sonora Move on the crest of the Sierra Nevada. 

The latite is dark-colored with phenocrysts (crystals) of plagioclase feldspar scattered all through. It superficially resembles basalt, however is extra carefully associated to extra silica-rich lavas like andesite and dacite. The lava flowed down a river channel carved out of the tuffs and mudflow deposits of the Valley Springs  and Reduction Peak formations, ending someplace simply west of Knights Ferry, having traveled some 60 miles. The lava resisted erosion higher than the softer surrounding rock, and the circulation ultimately was exhumed, forming a winding, sinuous ridge, particularly within the neighborhood of Jamestown and Columbia.

Quickly after takeoff, we strategy Knights Ferry. The fashionable Stanislaus River makes a outstanding loop, with orchards and agricultural fields on the left-side flood plain. The upper terraces are drier, and are used primarily for grazing. The uncovered rocks within the barren areas are principally Mehrten formation, which consists of volcanic mudflow deposits round 4 to 9 million years previous.

North of Knights Ferry, exposures of the Gopher Ridge volcanics are seen. These are metamorphic rocks relationship from the Jurassic interval. These rocks shaped as island arcs (volcanic islands like Alaska’s Aleutian Islands) on the oceanic crust of the Pacific Ocean, however had been scraped off towards the sting of the North American continent because the rocks had been subducted. The rocks have been metamorphosed, and turned nearly vertical by intense east-west strain. They’re extra resistant than the encircling slates, and so stand out as a outstanding ridge. The city of Copperopolis is barely seen within the higher proper nook of the picture.

Farther alongside, we move the positioning of the Harvard Mine. The open-pit mine was energetic from 1986 to 1994, producing about 660,000 ounces of gold from about 17 million quick tons of rock. The lake within the pit is about 300 ft deep. Simply previous to closing down, the miners recovered an enormous mass of crystallized gold, weighing greater than 40 kilos. The gold is on show on the Ironstone Vineyard in Murphys. The physique of water within the background is New Melones Lake.

Our turnaround level was simply east of the city of Sonora. The city had its beginnings in 1848 when gold was found by Mexican nationals who had misplaced their citizenship as California was signed over to the US. The Mexicans had been quickly displaced (“invited to go away”) by American miners.  The unique city is seen within the center-right a part of the picture, whereas the newer city growth is seen within the middle and left-hand half. Scars from the on-going development (accomplished way back) of a bypass can be seen.

Turning west, we begin to see the inverted stream of Desk Mountain. Freeway 108 passes alongside the decrease left hand a part of the picture. Little or no soil has developed on the highest of the previous lava circulation (word the dearth of bushes, and broadly scattered grassy areas). The sinuous nature of the circulation is turning into evident.

A glance out the again of the airplane affords the very best view of the circulation. The barren-looking floor of the circulation is definitely a novel ecosystem of native wildflowers which are largely freed from the invasive European grasses which have overwhelmed the unique grasses over a lot of the area. It’s a fascinating hike, particularly within the spring after a couple of good rainstorms. A comparatively latest hike to the highest of the lava circulation will be seen right here: https://geotripper.blogspot.com/2015/04/where-rivers-are-upside-down-hike-to.html

Trying west, with Knights Ferry within the far distance. The circulation is wider, particularly the place a number of the lava backed up into some historical tributary streams. Tulloch Lake on the Stanislaus River is seen to the suitable.

The remainder of the flight was a bit extra mundane, as we buzzed my home and returned to Oakdale.

My due to Ken Iwahashi, the pilot on our journey.