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Before our work in western Grand Canyon began in the mid-1990s, nearly all the age constraints on lava flows relied on a technique called potassium-argon dating, also known as K-Ar ages. K-Ar ages rely on the radioactive decay of potassium to argon gas. K-Ar ages of western Grand Canyon lava flows range from 10,000 years (Vulcan’s Throne) to 1.8 million years (Prospect Dam).
Because the lava was bringing up and storing extra argon before it cooled into rock, measurements made by scientists made it appear that the lava had been rock for a much longer period of time than actually had transpired. New 40Ar/39Ar studies of western Grand Canyon lavas (Pederson et al., 2002; Luchitta et al., 2000; Mc Intosh et al., 2002) show the oldest lava flow, the Black Ledge flow, is approximately 600,000 to 650,000 years old. Turrin, Cyclic aggradation and downcutting, fluvial response to volcanic activity, and calibration of soil-carbonate stages in the western Grand Canyon, Arizona, Quaternary Research, v. The youngest flow (Esplanade Dam) dated with Ar/Ar or K-Ar techniques is 110,000 years old (Dalrymple and Hamblin, 1998). These protons cause a cascading shower of nuclear interactions in both the atmosphere and in the surface of rocks on the ground. The longer a rock has been exposed to these cosmic rays, the older the cosmogenic age of the rock.
Cosmogenic ages of lava flows on the Uinkaret Plateau range in age from 1,000 to 400,000 years and for the most part, agree with Ar/Ar ages of the same flows.