| Timothy H. O'Sullivan 13. Marble Canon, one of the gorges of the Colorado, here 1,200 feet deep. The steep cliff is gray limestone and the slope below a brilliant red sandstone. [Wheeler Survey, Explorations and Surveys West of the 100th Meridian] 1871-1874 (survey), 1872 (expedition) Stereocard, detail Etherton Gallery LL/24733
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