Compilation of Unpublished USGS and University of Arizona K-Ar Dates of Volcanic Rocks of the San Francisco Volcanic Field, Northern Arizona

This compilation reports 174 K-Ar dates from the San Francisco Volcanic Field in northern Arizona. Of these dates, 112 are from the US Geological Survey in Menlo Park, California, and 62 are from the Laboratory of Isotope Geochemistry at the Department of Geosciences, University of Arizona. Most of these dates have not been previously published and none are in the compilation by Reynolds and others (1986). Those that have been published have not included analytical data. Some of these dates have not been released because, for various reasons, it seemed likely that they did not accurately represent rock age. Dates reported here have all been recalculated using lUGS decay and abundance constants (Table 1; Steiger and Jager, 1977; see also Dalrymple, 1979). Potassium was measured by flame photometry using a lithium internal standard. Uncertainty in potassium analysis is either sample standard deviation or 0.5%, whichever is greater. Uncertainty of date, representing one standard deviation, was calculated by the method of Cox and Dalrymple (1967) assuming a standard deviation of 0.3 % for tracer calibration.