Following the retreating glaciers of the last glaciation period of the Ice Age, melt water accumulated in the closed basins of what now is south central Oregon. As a result, pluvial lakes covered much of the high desert. This included the Summer Lake basin south of Picture Rock Pass and the Silver Lake basin north of the pass. The marshes and meadows that surrounded these lakes were ideal habitat for wildlife including bison, deer, antelope, mountain sheep, and many varieties of waterfowl. The abundant wildlife drew prehistoric hunters to the area.