Figure Caption Microstratigraphies in rock varnish from radiometrically dated geomorphic features in the western US drylands. Age constraints are reported in cal yr BP (± 1 sigma) and letters in the varnish images correspond to those in the age calibration figure. Note that black layers WP0a and WP0b in (A) are optically merged as one major basal dark layer, but chemically they are identified as two Ba-rich peaks in the microprobe line profile. Please see Liu (2003, 2007) and Liu and Broecker (2006) for more discussion on this topic. WH = Wet event in Holocene, WP = Wet event in Pleistocene.