Over 200 isolated outcrops of horizontally stratified, basaltic lava flows within the inner gorge of western Grand Canyon indicate that several natural "lava dams" blocked the flow of the Colorado River during the Pleistocene, resulting in the formation of several lakes within the canyon. The largest lake was 90 m above the high water level of present-day Lake Powell and backed up a distance of over 480 km to Moab, Utah . Although early studies indicated that three or less dams once blocked the inner gorge, work completed in 1994 indicated that at least 13 distinct lava dams may have blocked the Colorado River. Comparison with modern erosion rates of cliff retreat (Niagara Falls) indicate that the 13 dams would have required a minimum of 250,000 years to erode during the Pleistocene. However, geologic features and relationships not previously considered indicate that the dams formed rapidly (hours, days, or months) and failed catastrophically soon after formation. Excess radiogenic argon is contain within many basalts of Grand Canyon. This initial argon invalidates K-Ar model ages which are assumed by many geologists to require an age of more than one million years for the oldest lava dams. We envision that the entire episode of the lava darns can easily be reconciled within a time-frame of less than two thousand years. Our observations and interpretations reveal serious flaws in the current long-age timescale of the Pleistocene Epoch.
