Historic Resource Study, Crater Lake National Park, Oregon, 1984
I. Formation of the Crater Lake Environment
B. Prehistoric Indian Occupation of the Crater Lake Vicinity
Man’s initial entry into the now arid basins stretching from south-central Oregon to southeast California began about 10,000 years ago, after the end of the volcanic activity characterizing the last Ice Age (Pleistocene glacial epoch), when, although deep snowfields and glaciers blanketed the lands northward toward Canada, here in the Plateau area a more benign climate, inland lakes, and dense forests offered a relatively comfortable existence for groups of nomadic hunters. Natural shelters at the bases of high cliffs and small caves found today high above present water levels have yielded evidence of human occupation in the form of stone and bone tools and weapons and grinding stones dating from at least 13,000 years ago.  The first inhabitants of the Klamath-Tule Lake basins, arriving between 7,500 and 10,000 years ago, showed a more specialized lifestyle and culture; the greatest mass of evidence of human presence in this area dates from this time period. Abundant springs provided water, and cultural remains indicate a simple hunting and seed- and root-gathering existence.
The eruption of Mount Mazama 6,600 years ago probably only hastened an abandonment of the cliffs that had already begun with the advent of warmer temperatures in 11,000 B.C. The eruption was undoubtedly witnessed by humans, a never-to-be-forgotten occurrence immortalized by detailed and descriptive legends. That man was nearby at the time is attested to by archeological investigations at Fort Rock Cave about fifty-five miles northeast of Mount Mazama in 1938 that uncovered one hundred woven-sagebrush sandals covered, baked, and charred by the mud flow and ashes from Mazama’s eruption.  For miles around plants would have been buried and burned and lakes and marshes clogged, suffocating the fish population and depriving upland game birds and waterfowl of sanctuary.
With living conditions so difficult, human activity here probably ended for several centuries. The climate continued to change; annual rainfall lessened, evaporation from lake surfaces increased, and water levels consequently began to recede. Plant life thrived, however, and grass became more prevalent, indicating an ecological environment somewhere between the moist, cool forest and the drier desert extreme. As the grassland spread and lakes and marshes dwindled to only scattered springs and seeps, making dependable water sources scarce, the ancestors of the historic Klamath and Modoc peoples, who drifted back into southern Oregon and northern California focused on the lakes, streams, and marshes for their homesites. To replace the earlier cave dwellings, small permanent winter hamlets were constructed on high ground near the water. As the climate and the land continued to change, lifestyles of necessity became more diversified and ultimately specialized. The large numbers of fishhooks and manos, metates, and mortars for pounding, grinding, and milling seeds and roots found by archeologists confirm a growing dependency on the water and plant foods for nourishment. Increased population shifts, facilitated by a friendlier climate, inevitably resulted in an exchange of techniques relative to both technological processes and food acquisition. By 4,500 years ago, environmental conditions were fairly stable and the customs and living patterns developed that were present when whites arrived.