Ice-Rafted Erratics - 2 Minute Geology

Two-Minute Geology. The Two-Minute Geology. Hello, young people. Ice-rafted erratics near Mattawa, Washington. Erratics. Boulders that do not match the local bedrock. The local bedrock here in central Washington is brown. Layers of basalt, lava rock, and yet we've got these big light-colored boulders, granites, and metamorphic rocks that dot the landscape. How did they get here? Erratics are usually associated with glaciers, ice sheets, bringing these boulders to an area. But here at Mattawa, we are 60 miles south of where the ice sheet used to be in north-central Washington, north of Wenatchee. So this is not from glacial activity. This is from Ice Age floods, ripping off pieces of that ice sheet and carrying these boulders down here. Ice-rafted erratics. Let's go a little further south in the Pasco Basin and look for more of these guys, okay? How about this beauty? We're on the lower slopes of Rattlesnake Mountain near Benton City, Washington. This is argillite, a metamorphic rock that used to be shale. 1.5 billion years old. This thing's like 12 feet long. It's angular. The Ice Age floods brought this boulder here. This is Rocky Mountain geology brought to south-central Washington. Rafts of ice, icebergs, floating in the water, carrying boulders like these. This guy either fell off of its ice raft, or the iceberg got into some quiet water, stranded, melted, and left the rock. Regardless, this boulder's been sitting here for at least 13,000 years. Ice-rafted erratics in south-central Washington. It's all out here to see Cooleys, rocks, and canyons, it's scenery Right here for you and me. Two Minute Geology.