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Introduction The purpose of this presentation is to To the right are the PDSI plots for the compare and contrast the settlement his- Climatic Extremes and Human Resilience: two hydrographic basins. The tree ring tories of two large hydrographic basins data indicates some moist periods in the in the Great Basin of Nevada and Cali- An Examination of Two Hydrographic LHD, and confirms the 18O core data fornia. Basins in the Great Basin for the LALIA and MCA. Both PDSI The one basin is the Black Rock Desert plots also show moderate drought dur- Basin (HUC-6 160402) and the other is (northern Nevada, USA) ing the LIA (PDSI values less than –1). Another indicator of drought in the LIA the Truckee Basin (HUC-6 160501). is the decreased Artemesia/ The Black Rock Desert Basin covers over 2.1 million hectares in NW Neva- Mark E. Hall (Black Rock Field Office, Chenopodiaceae ratio in the Mud Mead- da and ranges in elevation from 2000 m Bureau of Land Management ows/Soldier Meadows pollen core (below). to 1100 m. The Quinn river flows 180 [email protected]) km from the Montana Mountains to the https://orcid.org/0000-0003-2089-9271 Black Rock desert playa where it forms DOI: 10.5194/egusphere-egu21-13370 a seasonal lake. The Truckee Basin ranges in elevation from over 2200 m to 1200 m. This ba- Palaeoclimate Data sin covers approximately 1.2 million hectares. The Truckee river flows 195 km from Lake Tahoe to Pyramid Lake. It is noted that these two basins were Spatio-Temporal Patterns connected during the highstand of Lake Lahontan. They have been separate ba- sins since ca. 9800 BP. In terms of ecoregions, these basins are split between the North and Central Basin and Range re- gions, and are classified as a cold desert. The ReGap database notes that the vegetation commu- nities at lower elevations consists of mixed salt brush and desert scrub, greasewood, and relative- ly unvegetated playas. Higher elevations are dominated by sagebrush communities, with some juniper in the Jackson Mountains. Gaussian kernel density maps are generated for various points in time to illustrate the spatial patterning of the radiocarbon dates. The heat maps are standardized for ease of comparison. Occupation at 10000 BP occurs around Winnemucca Lake in the Truckee Basin, and the tablelands surrounding Virgin Methodology Creek, the Jackson Mountains, and the northern end of the Black Rock Playa for the Black Rock Desert Basin. There are over 2000 prehistoric sites in the two hydrographic basins. Over the decades, hun- dreds of sites have been excavated, but only 87 sites have yielded materials for radiocarbon da- Above is the oxygen isotope data from Pyramid lake core 98-4. Dates are based on Benson’s revised 2014 dating. The dark heavy line is a 10 yr running mean spline fit through the data ting. While some of the excavations have been reported in the peer-reviewed literature, most have come from excavation reports that were written to fulfill the legal requirements under Sec- set. The dotted red lines are the extreme values for the upper and lower limits of the data set. tion 106 of the National Historic Preservation Act. These “grey literature” reports are primarily These were calculated using a non-parametric kernel density estimate (a generalized pareto- on file at the Carson City District Office (CCDO) or the Winnemucca District Office (WDO) of normal density model fit the data poorly). the Bureau of Land Management (BLM), but some are also on file with the Humboldt-Toyaibe Features to note in the 18O data set: 1) the aridity increases after the Mt. Mazama eruption; or Tahoe National Forest . 2) aridity increases during the 4.2 kya event; 3) wide range of dates for the rising lake levels at Lake Tahoe are in part due to the large radiocarbon standard deviations of the drowned tree The dataset for this study consists of 496 radiocarbon dates from 87 sites. Approximately a samples. sixth of the dates come from two sites—Elephant Mountain Cave and Last Supper Cave in the Black Rock Desert Basin. The dataset does not contain any radiocarbon dates from tufa, shells, or fish bone. No radiocarbon dates were rejected due to the size of the dating error; most radio- carbon dates have a standard deviation of less than 100 radiocarbon years. While “old wood” could be an issue for dates on charcoal, juniper growth is confined mainly to the Granite Range and the Jackson Mountain areas in the Black Rock Desert Basin. In the case of the Jackson Mountains, there are junipers growing there that are just over 1000 years old. Radiocarbon cali- Occupation contracts and is at a lesser intensity in both hydrographic basins at the 8.2 kya event. By 6800 BP, occupation is on the upswing. In the Tahoe Basin, Pyramid Lake and Winnemucca Lake are the foci of hunter-gatherer use. In the brations utilized the InterCal20 calibration curve; a taphonomic correction was not performed Black Rock Desert Basin occupation is still in the Jackson Mtns., and the Long Valley area sees use. when constructing SPDs. The location of the sites were confirmed in either the WDO cultural GIS database, or the Neva- da State Historic Preservation Office’s GIS database. The Mud Meadows/Soldier Meadows pollen core data is on file with the WDO. The summer Palmer Drought Severity Index (PDSI) data was obtained from http://drought.memphis.edu/ NADA/ for the region 40.5 to 42 degrees North and 119.75 to 118 degrees West. The recon- 18 The above figure is the O data set from core 97-1 from Pyramid lake covering the late Holo- struction of the PDSI was by Cook’s “Point-by-Point” ensemble regression method. The Pyra- cene. Note the increasing aridity through the Late Holocene Drought (LHD), likewise for the mid Lake oxygen isotope data is available from NOAA at Late Antique Little Ice Age (LALIA). Note the extreme wet phase in the Medieval Climatic Anomaly (MCA) . Statistical analyses are done in R (R Core Team 2020). Spatio-temporal maps were created us- ing rcarbon (Crema and Bevan 2020). Radiocarbon calibrations utilized the InterCal20 calibra- tion curve, while age-depth modelling for dating the pollen core was done using Bacon. Other packages from R that were utilized include: evmix, Hmisc, maptools, and spatstat. At 900 BP, during the MCA, hunter-gatherer use is throughout both basins. In the LIA, there is a contraction in the use/settlement areas—for the Truckee Basin, sites are focused along the Truckee river and the major lakes. For the Black Rock Desert Basin, use shifts to the upland areas. .

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