August 20-23, 2008
Click on the small picture to see an enlargement.
|Steve Lipshie describes for the group the Bishop Tuff in Owen's Gorge. The tuff unit that the road is cut into and that is behind Steve's back is the same as the lower ash flow (ignimbrite) that we saw in the quarry on day 2, but immensely thicker here nearer the source. The thin white unit deposited in the swale over Steve's head is the same as airfall ash number 2 that we saw in the quarry, but much thinner here, perhaps due to erosion by the overriding upper ash flow. The ash flow above the swale corresponds to the upper ash flow in the quarry.
||In this photo Steve is pointing to the unusual pattern of radiating columnar joints that formed in the Bishop Tuff as it cooled. These were unlike anything we had seen before.
||Jeff DeBoo and Matt Raimo get a closeup look at the Bishop Tuff, that contains pumice fragments, phenocrysts of sanidine, quartz, and plagioclase, and xenoliths of basalt, hornfels, quartzite, and granitoids. The xenoliths indicate the nature of the basement rocks through which the eruption occurred.
||Here John Johnson uses his little hammer in an attempt to collect part of one of the humongous columns of Bishop Tuff. After breaking it free, it would not fit in his pocket, so he left it behind and settled for a tiny piece.
||In this photo, the group stands on the rim of the southernmost of the Inyo Craters and listens while Steve explains their origin. The craters probably are phreatic explosion pits created when rising magma encountered ground water and vaporized it, causing an explosion when the vapor pressure exceeded the weight of the overlying rock.
||View of the southernmost of the Inyo Craters and the green lake inside of it. The cliffs around the crater are made of an andesite flow that is older than the crater and through which the phreatic explosion occurred. The hill in the background is a dome of hornblende-biotite rhyolite that has been dated at about 100,000 years old.
||Here the group is looking into the second lake-filled crater. Based on the amount of volcanic activity in the Mammoth Lakes area in the last 500 to 600 years, it seems probable that such activity will continue into the future.
||We ate lunch along the shore of Convict Lake. Enjoying the shade at this picnic table, from left to right, are Howard Brown (longest beard awardee), Chuck Real, Steve Lipshie, Mike Ponek, Greg Farrand, Julie Lefever, Linda Ritterbush, Sandy Jewett, and Vicki Pedone (photographing the lake).
||In the parking lot at Convict Lake, Paul Stone (white hat by driver's door) told us about the Mount Morrison roof pendant,that is across the lake in the direction we are all looking.
||Rocks in the mountain behind Convict Lake are in the Mount Morrison roof pendant. Facing the camera is Chuck Real who is telling us about the earthquake swarm that occurred in the vicinity several years earlier.
||Our last stop for the day was at McGee Creek, where we looked at the McGee Creek glacial moraines and a fault scarp that cut the moraines and also took a short hike up the canyon to look at rocks in the moraines.|
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THIS PAGE LAST MODIFIED ON SEPTEMBER 27, 2008
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