Paleomagnetic data from Miocene ash flow sheets indicate that southern Yucca Mountain has undergone about 30?? of clockwise vertical-axis rotation since emplacement of the Tiva Canyon Member of the Paintbrush Tuff at about 13 Ma. Declinations of remanent magnetization from 32 sites in the reversely magnetized Tiva Canyon member display a systematic southward increase over the 25 km north-south extent of Yucca Mountain. Analysis of tilt-corrected directions of remanent magnetization from the Tiva Canyon sites indicates that structural attitudes determined from outcrop patterns on geologic maps are generally more accurate than field measurements of attitudes of compaction foliation or contacts. -from Authors