In conclusion, I would like to endorse Moratto et al.'s proposal that climatic change studies be closely coordinated with archaeological research wherever possible. In California the prospects for such cooperation are good and certainly there is no shortage of interesting problems.

This dissertation focuses on the spatial distribution of five climatically sensitive plant taxa in central and northwestern Mexico during three time periods: the present, the mid-Holocene and the Last Glacial Maximum (LGM). The results presented here are rooted in recent methods of bioclimatic envelope modeling that incorporate high-resolution paleoclimate model data, GIS, online herbaria data, and cartography. Although the paleoclimate model data and computer methods used in this work are crucial to its outcome, the validation of the model results for the mid-Holocene and LGM rests largely on paleoecological evidence from Mexican fossil pollen sites. In this dissertation, I have devoted much of the discussion to how well the modeled results agree with the paleoecological records and interpretations.

The majority of fossil pollen sites spanning both the mid-Holocene and Last Glacial Maximum occurs in the northwest and central regions of Mexico. The concentration of these sites led to the narrowing of what spatial distribution to consider in the modeling efforts. In both central and northwestern Mexico, there are plant taxa that appear today whose presence has varied over time as environmental conditions fluctuated. The five plant taxa modeled here are Abies, Artemisia, Liquidambar, Picea, and Taxodium, all significant taxa in the pollen record as indicators of temperature and moisture change. In the cases of Abies, Picea and Artemisia, multiple species occur throughout Mexico, which complicates the construction of a climate envelope. In these instances, only one species was modeled in an effort to minimize conflation in the results, which may have happened if multiple species were considered.

The first segment of the work focused on constructing and validating one model for each taxon in the present. The most realistic models from the effort were those for Abies religiosa, Picea chihuahuana and Liquidambar styraciflua, each having very narrow climatic requirements, and occurring in definable biogeographic regions of Mexico. The success also speaks to the appropriateness of species choice, the accuracy of the climate model data as well as the performance of the bioclimatic envelope model. The two models that performed less desirably were those of Taxodium mucronatum and Artemisia ludoviciana. The broad distribution of Artemisia presented challenges in pinpointing an appropriate set of climate parameters for the envelope construction. T. mucronatum is dependent upon flooded riparian pathways for reproduction, an aspect of the environment that was not included in the model construction. Since only bioclimatic parameters were included, the resulting model reflects a clear lack of agreement between the predicted and actual distribution. These results illustrate the importance of selecting an appropriate species for envelope modeling methods.

The second segment of the work was that of projecting the present-day models into the past. Predictably, the three accurate present-day models also performed well when projected into past climate data while the other two models did not agree well with paleoproxy data. However, Picea's mid-Holocene model did generate surprising results by appearing in the central Mexican region. Pollen evidence of Picea in central Mexico during the mid-Holocene is extremely rare and unlikely. Also, some disagreement did appear between the fossil record and the modeled distribution for Liquidambar. According to the fossil record, Liquidambar did appear in the Mexican Basin during the mid-Holocene, but the model does not reflect that finding. The reasons for the disagreement may lie in the variable selection for the envelope, the climate model data, or more likely, the inability of this broad scale technique to model local conditions that may have influenced Liquidambar's distribution.

Finally, the last portion of the work was an experiment comparing species distribution models produced using different climate models modified using EOF analysis. The goal was to determine how, if at all, the ecological models differed from one another. The results indicate some effect, though not particularly significant ones at the broad scale of this work.

In summary, the main finding of the research is that modern bioclimatic modeling techniques with high-resolution climate data are useful in generating paleoecological distributions, but with the following constraints, 1) an appropriate taxon with an easily-defined climatic envelope is modeled, 2) researchers complete a thorough comparison between the model results and palynological records to confirm or refute a models' validity.

Dramatic environmental changes have occurred in the last 50,000 years in California due both to changes in climate and anthropogenic impacts. Analyses of pollen and microscopic charcoal from sediment cores from three wetland sites in central California record changes in vegetation and fire frequencies during the late Pleistocene and Holocene at different temporal resolutions. A long-term record with a basal date of ca. 50,000 cal yrs BP from a coastal wetland north of Santa Cruz shows important vegetation shifts between the Last Glacial Maximum, the glacial-interglacial transition, and the mid- to late-Holocene, as well as the introduction of a frequent fire regime in the Holocene. A 3,000-year record from a wetland near Año Nuevo State Park provides evidence of an increase in fire frequency in coastal California from the fifteenth century to the present, and vegetation changes associated with logging after Euro-American settlement. A core that spans the last ca. 700 years from an oxbow lake in the Sacramento Valley records the introduction of non-native plants into the area after European arrival. Together, these records help place the magnitude of anthropogenic impacts in the context of long-term environmental change due to regional or global climatic forcing.

This study focuses on the history of natural and human-induced environmental change as recorded in the sediments of two lakes: Mountain Lake in the Presidio National Park, San Francisco, California and Big Soda Lake, near Fallon, Churchill County, Nevada. The records of these lakes examined in this study cover approximately the last 2,000 years. Sediment cores from the lakes were dated with radiocarbon, lead-210, plutonium 240/239, tephrachronology, and the first appearance of non-native pollen types. The cores were analyzed to determine changes in stable isotopes (carbon and oxygen), sediment chemistry, fossil pollen, magnetic susceptibility, organic content, and brine shrimp cyst concentrations.

Big Soda Lake has been the subject of scientific investigation since the 19th Century and two famous scientists have previously worked at the site. First, the geologist, Israel Russell explored the lake in 1882 as part of his work on Pleistocene Lake Lahontan and provided the first scientific report on the lake. Later in 1933, Evelyn Hutchinson, the famous Yale limnologist, provided the first detailed limnological report for the lake. More recently in the 1980's, the lake has been studied by scientists from the United States Geological Survey. However, prior to the research reported on here, very little was known of the history of the lake or to what extent its sediments contained a useful record of environmental change.

The sediments of Big Soda Lake provide clear evidence for both natural and human-induced environmental change during the past 1600 years. The climate record developed from the analyses of stable isotopes of oxygen and carbon, sediment chemistry, and the concentrations of brine shrimp cysts show several significant shifts in climate. The early part of the record from A.D. 400-850 is period marked by a fluctuating climate, with alternating wet/dry phases each lasting several decades each (40-60 years). During the period known as the Medieval Climate Anomaly (MCA)(A.D. 850-1400), we observe at least two relatively dry periods from A.D. 850-1150 and A.D. 1260-1400. Between the two dry phases, there is a pronounced wet period from A.D. 1150-1260. This wet period matches fairly well with evidence presented in other paleoenvironmental studies in the western Great Basin. During the Little Ice Age (LIA), the evidence indicates that the Big Soda Lake area was not always colder and/or wetter, but that it was in fact drier and perhaps warmer from A.D. 1400-1700 than it had been in the previous millennium. Pronounced dry phases were observed around A.D. 1400, A.D. 1500 and A.D. 1650. The wettest period during the LIA came between A.D. 1750-1800.

The human impact record at Big Soda Lake developed from the analyses of stable isotopes of oxygen and carbon, sediment chemistry, and the concentrations of brine shrimp cysts show several dramatic changes in and around the lake since Anglo American settlement of the area began, in the 1850's. Several human impacts have been identified, including regional mining activity, soda salt extraction from the lake, and irrigation induced rising groundwater levels in the last century. Two of these events have dramatically impacted the lake in that time. Firstly, the development of a commercial soda manufacturing and processing facility at the lake beginning in 1875 until the early 20th century; and secondly, the development of irrigation agriculture which led to an 18 m rise in lake level in the first few decades of the twentieth century.

The sediments at Mountain Lake provide evidence of unprecedented heavy metal contamination at the San Francisco Presidio during the past 60 years. The lake evidence is consistent with local land-use changes initiated by the arrival of Europeans in the area after 1776 and the construction of California State Highway 1 adjacent to the lake in the late 1930's. The study shows how small water bodies alongside roads can concentrate heavy metals and demonstrates the need for careful scientific investigation of sediments earmarked for dredging to determine what if any contaminants are present.

A key outcome of the Mountain Lake research carried out as part of this dissertation was that in the Fall of 2011 a Federal judge ordered the California Department of Transportation (Caltrans) to pay 13.5 million dollars to the Presidio Trust so that the contaminated sediments could be removed and further run-off from the road be prevented from entering the lake.

Sediment cores were raised from fringing marshes along the northern reach of the San Francisco Bay. A variety of stratigraphic analyses were utilized to reconstruct sea level and river flow (salinity) over the past 7000 yr. Over thirty A.M.S. dates provide chronostratigraphic control. An overall trend in RSL rise of 0.12-0.14 cm/yr is established for the northern reach of the estuary. River discharge was broadly comparable to modem flows. However, an extended period of higher flow commenced approximately 3800 yr and continued for almost 2 millennia. Superimposed upon these general trends are numerous short-term events. Acute droughts and salinity intrusion occurred during the period of high river flow. No extreme flood events are noted during this period, although evidence for abnormally high discharge occurs at other times.

In this paper, we report on a second attempt to recover pollen from the Leonard Rockshelter sediments. In 1976, we directed our attention to two series of samples that included the whole of the stratigraphic sequence. The samples were collected during the 1950 excavation, and had since been stored in the Lowie Museum of Anthropology (Berkeley). Like Hansen, we found it impossible to extract pollen from the lower bat guano layer, but the overlying silt and rockfall layers yielded reasonably well-preserved pollen in countable quantities. The results of the analysis in large part support the Antevs model and also throw new light on the "significance" of climatic change in the Great Basin.