This thesis reconstructs the landscape evolution of the Billy Big Spring site (24GL304, Glacier County, north-central Montana) from the last glacial maximum to present through the analysis of sediment and soil samples collected from a transect of auger tests that bisected the site and surrounding landforms. Interpretations were drawn from stratigraphy, pedologic data, sedimentologic analysis and radiocarbon dating. The site landscape came into being in the late-Pleistocene, after Wisconsin-age glaciers retreated. Glacial retreat left a meltdown depression on the land that filled with water to form a pond, which persisted through the early-Holocene. The onset of the mid-Holocene (Altithermal) occurred before ~8,415 cal. yrs. BP, when increasingly arid conditions caused the water level to drop. The first radiocarbon dated human occupation of this site occurred during the Altithermal, ~7,030 cal. yrs. BP, after the eruption of Mount Mazama (~7,633 cal. yrs. BP). Arid conditions continued until ~7,000 cal. yrs. BP, when pond water re-expanded across the basin, marking the transition to the cooler late-Holocene. Sometime before 2,100 cal. yrs. BP, dry conditions returned, and the extent of the pond water decreased again. Since this time, overland alluvial processes have deposited sediments in the basin. Many hypotheses on how the Altithermal impacted the people of the Northwestern Plains have been proposed since the 1950s, but little agreement has been reached. This is due to the fact that there was great variation in how the Altithermal expressed itself throughout the Northwestern Plains. The human reactions to this phenomena cannot be explained simplistically for the region as a whole. This study shows that the Billy Big Spring site experienced drying during the Altithermal, but despite this, people continued to occupy this site. This evidence adds to the argument that the Altithermal climate of the Northwestern Plains did not have severe enough impacts to impose much hardship on its occupants.