Figure 11    Colluvial boulder deposits of welded tuff on the west slope of Yucca Mountain, southern Nevada (A) and optical varnish microstratigraphy in a varnish sample from the largest boulder stripe (about 60 m long) on the slope (B). The VML age estimate of 46 ka is based on our preliminary layering pattern interpretation and the varnish age scale given in Fig. 6. Note that other similar boulder deposits at Buckboard Mesa in the same area were cosmogenically ³⁶Cl dated at ~ 660 ka (Whitney and Harrington, 1993; see text for discussion). LU = layering unit, WP = wet event in Pleistocene.