Stop #3 (10:45 a.m.) - Lyons formation at top of hill beyond trees. Roadcut in foreground is a more modern debris flow. We know it's a debris flow because the larger rocks and boulders are on the top with the fine grained material below. This is common in debris flows and avalanches.
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"Colluvium" - gravity moving rocks so bigger rocks are on top in debris flow. (Like the "Gorp" effect where the larger nuts move to the top of the bag while the smaller go to the bottom.)
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Top of the Fountain formation. Well sorted, finely grained, formed by wind blowing sands and creating dune fields. There are alternating layers in the last 30 meters of the Fountain formation caused by alternating wind and water making dune, river, dune, river. Looking closely at these rocks, you can see thin horizontal "sand sheets" which are at the margins of the sand dunes.
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Note tiny white and gray pebbles sitting on sand dune surface. These are called "lag sands" and are evenly spaced on the surface. Caused by wind blowing pebbles along and breaking them up some as they bounce along. This even spacing only occurs in dune deposition, not river.
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Holes are where hematite (secondary) has weathered out of the Fountain sandstones.
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This is the contact between the Fountain & Lyons formations. The bottom of the Lyons formation is near the top of the picture (thinner, flat cross bedding). The top of the Fountain is just below it, extending to the base of the image.
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The Lyons formation is all sand dunes. It is very finely grained and evenly sorted. The Lyons is still a pinkish color like much of the Fountain, but it is quartz cemented by quartz which gives it a shiny surface.
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The Lyons formation is often has large wedge shaped bedding which is common in sand dunes. Breaks in concoidal fractures because of quartz cemented by quartz.
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Lyons formation is quartz cemented by quartz makes the very sparkly surface. (unfortunately not in focus).
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Thin laminations of ancient sand dunes of the Lyons. If you look closely with a hand lens, you can see the wind deposited sands in each of the thin sheets with small grains at the bottom of each and larger grains at top (very fine up to medium at top of lamination).
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Cross bedding of Lyons formation's sand dunes
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Cross bedding of Lyons formation's sand dunes
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Small raised areas are the result of raindrops hitting the surface of the adjancent sand. Then, this sand layer covered the other sand and filled in the holes, making these inverted (raised) raindrop marks. (This is the bottom surface of the rock)
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Small raised areas are the result of raindrops hitting the surface of the adjancent sand. Then, this sand layer covered the other sand and filled in the holes, making these inverted (raised) raindrop marks. (This is the bottom surface of the rock)
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