In Curry County, the lower Rogue passes through the Galice Formation, metamorphosed shale and other rocks formed when a small oceanic basin in the merging Klamath terranes was thrust over other Klamath rocks about 155 million years ago. The lowest part of the seafloor of the Josephine Basin, as this ancient sea came to be called, rests on top of the Kalmiopsis Wilderness, where it is known as the Josephine ophiolite. Some of its rocks are peridotite, reddish-brown when exposed to oxygen but very dark green inside. According to geologist Ellen Morris Bishop, “These odd tawny peridotites in the Kalmiopsis Wilderness are among the world’s best examples of rocks that form the mantle.”[24] Metamorphosed peridotite appears as serpentine along the west side of the Illinois River.[24] Chemically unsuited for growing plants, widespread serpentinite in the Klamaths supports sparse vegetation in parts of the watershed.[21] The Josephine peridotite was a source of valuable chromium ore, mined in the region between 1917 and 1960.[24]
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