ABSTRACT Sedimentary records were analyzed from three lakes in the Ruby Mountains and East Humboldt Range of northeastern Nevada. Lakes are rare in the arid Great Basin, and these represent the highest-elevation lacustrine records from this region. The three cores cover overlapping time intervals: One, from a lake located just beyond a moraine, is interpreted to represent the Last Glacial Maximum, extending back to 26 cal ka; another extends to deglaciation ca. 14 cal ka; and the third extends to deposition of the Mazama ash, ca. 7.7 cal ka. Multiproxy analysis focused on measurements of bulk density, organic matter content, C:N ratio, biogenic silica abundance, and grain-size distribution. Depth-age models were developed using optically stimulated luminescence (OSL) dating, along with accelerator mass spectrometry (AMS) 14 C dating of terrestrial macrofossils (wood and conifer needles), charcoal, and pollen concentrates (for deep sediment in one lake). Collectively, the three lakes record a series of discrete intervals spanning an unusually long stretch of time. These include the local Last Glacial Maximum (26.0–18.5 cal ka), local deglaciation (18.5–13.8 cal ka), the onset of biologic productivity (13.8–11.3 cal ka), early Holocene aridity (11.3–7.8 cal ka), deposition and reworking of the Mazama ash (7.8–5.5 cal ka), a neopluvial interval (5.5–3.8 cal ka), a variable late Holocene climate (3.8–0.25 cal ka), and a latest Holocene productivity spike (250 yr B.P. to the present) that may be anthropogenic. Data from all three lakes are presented, and the collective record of climate and environmental change for the Ruby Mountains and East Humboldt Range is compared with other paleorecords from the Great Basin.

ABSTRACT The field trip examines coupled hydrologic and landscape response after the cataclysmic eruption of Mount Mazama to form Crater Lake in the Cascade volcanic arc at ~7627 ± 150 cal. yr B.P. The Williamson River basin, east of Crater Lake and in the rain shadow of the Cascade Range, was buried beneath thick pumice and pyroclastic-flow deposits. The distinctive physical properties of pumice and volcanic ash affect the movement and retention of water and the ongoing evolution of the landscape. Three themes will be explored: (1) post-eruption transition from perched streams to losing streams along the eastern flank of the Cascade Range; (2) filling and catastrophic draining of a lake trapped behind a dam of pyroclastic flow deposits in the Williamson River canyon; and (3) post-eruption faulting and the hydrology of Klamath Marsh.