Sign is located on Ore. State Hwy. 31 at milepoint 28.95.
New (2007) Marker Name: Fort Rock
New (2007) Marker Text: Fort Rock is the remnant of a maar volcano or tuff ring, formed when rising basaltic magma encountered water and exploded violently. The exploded debris -- called tuff -- fell back to earth around the volcanic vent to form this steep-walled, fort-like ring. Over time, the basin filled with a shallow lake, which breached the south rim of the tuff ring and cut a terrace about 60 feet above the floor of the valley. A State Monument and a National Natural Landmark, Fort Rock is one of several maars in the area; other examples are Hole-in-the-Ground, Table Rock, Flat Top, and Big Hole. Look ahead of you to the east for a view of Fort Rock in the distance.
Original Marker Name: Fort Rock
Original Marker Text: Some of the earliest known inhabitants this continent make their home in the cave in one of the low knolls dominated by Fort Rock visible across this basin. Radiocarbon dating indicates that sandals found in the cave may be 9,000 years old. Fort Rock is the remnant of an ancient volcano rasing 325 feet above the plain. A great lake covered this entire basin spreading as far south as Picture Rock. It was in a cave facing that lake that the Fort Rock people lived.
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