Alluvial fans are built in response to erosion induced by tectonic uplift, and upwards coarsening of beds reflects cycles of erosion in the highlands feeding sediments to the fan. However, climate and changes in base level may be as important. Alluvial fans in the Himalayas show older fans entrenched and overlain by younger fans, which in turn are cut by deep incised valleys showing two terrace levels. Dating via optical stimulated thermoluminescence (OSL) suggests a hiatus of 70 to 80 thousand years between the old and new fans, with evidence of tectonic tilting at 45 thousand years ago and an end to fan deposition 20 thousand years ago. Both the hiatus and the more recent end to fan deposition are thought to be connected to periods of enhanced southwest monsoon precipitation. Dating of beds in Death Valley suggest that peaks of fan deposition during the last 25 thousand years occurred during times of rapid climate change, both from wet to dry and from dry to wet.