Geo 730: April 29, Day 485: Sign of a Map

Another one of the interpretive signs at the beginning of the trail up to Erratic Rock, showing the general layout of the great floods that scoured the Pacific Northwest toward the end of the last glacial maximum. Judging from pages 16 and 17 of "Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon" (USGS Professional Paper 1620, PDF), in the Corvallis area the Missoula silts are about 4-5 meters in thickness, but thicken rapidly northward/downstream along the Willamette main stem. This site is well north of my home, but I suspect that up on the hill, where the erratic rests, the thickness is much less than here on the valley floor.

Photo unmodified. July 10, 2012. FlashEarth location.