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"Final report to National Park Service, Contract PX 8601-7-0106"

Prior research in the Rhyolite Canyon area of Chiricahua National Monument (Swetnam et. al. 1989) revealed an anomalous 50 year fire-free interval between 1901 and 1851. Disruption of fire spread resulting from flooding and mass soil movement (debris flows) were postulated as potential causes of this long interval. The present study gathered additional evidence of fire and floods in the canyon system. Sampling of flood-scarred trees along stream channels successfully identified several flood events in Rhyolite canyon. Pulses of pine regeneration on debris flow deposits were associated with one of these events. However, no definitive linkage of flood events with changes in fire regime was established. Analysis of new fire scar samples combined with previous results indicated that the area affected by the change in fire regime includes the uplands between Jesse James Canyon and Rhyolite drainage. Source areas for fires prior to 1900 were not identified within the study area indicating that ignitions outside the present monument boundaries may have been important in the past. Evidence from the maximum ages of overstory conifers within Rhyolite Canyon suggests the occurrence of a major disturbance within this drainage prior to 1600.

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"June 2000." / Includes bibliographical references (p. 61-62).

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No description available.

The tertiary history of the Chiricahua volcanic field of southeastern Arizona is essentially that of rhyolitic ash-flow deposition and concomitant block faulting in the period from 29 to 25 m.y., as determined by K-Ar analysis. The Rhyolite Canyon ash-flow sheet is the youngest of three sheets, each more than 1000 feet thick. Its distribution is limited mainly to the Chiricahua and northern Pedregosa Mountains with a lesser amount of deposits in the neighboring Swisshelm and Peloncillo Mountains. It is estimated that the original areal extent was of the order of 700 square miles and that the volume of deposits was around 100 cubic miles. The source area of the Rhyolite Canyon sheet is identified as a 13-mile diameter caldera, named the Turkey Creek caldera. This is the first major caldera of the Valles type described in the Mexican Highland and Sonoran Desert sections of the Basin and Range. It is unique because of its denudation. Erosion to 5000-foot depth locally has exposed thick sections of moat deposits and a fine grained monzonite pluton associated with central doming. Rhyolite Canyon tuff in the caldera, some 3000 feet thick, is domed and intruded by the monzonite. More than 1500 feet of tuff breccia, tuffaceous sediments, and rhyolite flows are exposed in the moat, along with 3000 feet of monzonite forming annular segments a couple miles wide abutting or overlying rocks forming the caldera wall. The most monzonite is similar to that in the dome and was emplaced amidst the period of deposition in the caldera. Petrographic and trace element analyses indicate a cogenetic relation between the Rhyolite Canyon sequence and the moat rhyolites. The K-Ar age of the Rhyolite Canyon tuff is very close to that of the monzonite. The ash-flow sheet immediately underlying the Rhyolite Canyon sheet is also very close in age as indicated by K-Ar analyses. Block faulting and tilting took place between the two sheets and also following the deposition of the Rhyolite Canyon sheet. There is evidence that the present basin-range structure was not established until after the Rhyolite Canyon sheet had been emplaced.