Columbia River Basalt Group map shows main regions of basalt exposure in Washington, Oregon, Idaho and Nevada, USA. (usgs.gov)- Deschutes River (Wikipedia)
The Deschutes River (/dəˈʃuːts/ də-SHOOTS) in central Oregon is a major tributary of the Columbia River. The river provides much of the drainage on the eastern side of the Cascade Range in Oregon, gathering many of the tributaries that descend from the drier, eastern flank of the mountains. The Deschutes provided an important route to and from the Columbia for Native Americans for thousands of years, and then in the 19th century for pioneers on the Oregon Trail. The river flows mostly through rugged and arid country, and its valley provides a cultural heart for central Oregon. Today the river supplies water for irrigation and is popular in the summer for whitewater rafting and fishing.