basin occupies portions of Jackson, Lake, and Klamath counties; in California, it flows through the counties of Siskiyou, Modoc, Trinity, Humboldt, and Del Norte (NRCS 2006).

For discussion and management, the Klamath basin is divided into the upper and lower Klamath basins. The generally accepted boundary between the two is Iron Gate Dam on the Klamath River. All lands upstream (that is, east and west) of the dam are within the upper Klamath basin (area: 8,060 mi²); and those below (that is, south and west of) the dam comprise the lower Klamath basin (area: 7,628 mi²). The lands within the upper basin fall within the U.S. Bureau of Reclamation (USBR) Klamath Project. A number of sub-basins are present throughout the watershed (Table 2-1). A large portion of the upper basin is in agriculture and rangeland use, whereas in the lower basin, forest land dominates the landscape with the exception of the Scott and Shasta basins which have large portions of area in agriculture and rangeland (Figure 2-1).

The largest towns in the basin are Klamath Falls, Oregon, which has a total metropolitan population of about 42,000 (City of Klamath Falls 2007); Yreka, CA (7,300), (Yreka Chamber of Commerce 2007); and Weaverville, California (3,550) (City-Data.com 2007). The basin is home to six federally recognized American Indian tribes: Yurok, Hoopa Valley, Karuk, Quartz Valley, Resighini (all in California) and the Klamath in Oregon.