The Mattole watershed is located in one of the most geologically active spots in North America. Three tectonic plates meet offshore, the North American, the Gorda, and the Pacific, forming the Mendocino Triple Junction. This network of faults produces many earthquakes, including the large and devastating events of 1952 and 1992. To learn about recent earthquakes in the area, click here.

Rates of uplift in the King Range are among the highest anywhere in North America. The Mattole watershed is underlain primarily by young sedimentary rocks, which are highly erodible and often incompetent - easily fragmented and cracked. Soils, which are primarily of the Atwell, Boomer, Cahto, Hugo, Josephine, Kneeland, Laughlin, Los Gatos, Mattole, Maymen, McMahon, Melbourne, Usal, Wilder and Zanone series, range in depth from less than a foot on rockier ridge tops to more than six feet in bottomlands.