Heritage: 25,000 to 10,000 years ago

Late Pleistocene Environment: 25,000 to 10,000 years ago

The nearer we get to the present, the more detailed is the information we have about the history of the environment. The plants and animals which existed became increasingly like those which exist today. The basic geography and geology of the area has not changed significantly in the last 25,000 years. The primary exception to this is the existence of glaciers in the mountains above 5,000 feet and the existence of lakes and extensive marshes in the lowlands. In general the climate was much cooler and wetter. The John Day Valley itself probably had a larger river and a more extensive marshy shoreline. Upland valleys like Bear, Logan and Fox had extensive marshes with potholes and lakes. Just to the south of the Forest, the lakes of the Harney Basin were all joined together into a giant lake almost five times as large as they are today. This ancient lake is known as Pleistocene Lake Malheur. The lake level fluctuated with changes in the climate and at times it rose high enough to flow into the Malheur River. Today the lakes in Harney County are part of the Great Basin and have no outlets to the sea.

The late Pleistocene vegetation differed from that of today primarily because it was adapted to a colder, moister climate. Sub-alpine and montane conifer forests of spruce, hemlock, larch, cedar, pine and fir covered the mountains and uplands. Mountain mahogany, wild cherry, buck brush and sage formed the forest understory. Grasses and sedges occurred both in forests and dry open areas. Cattails, tule, camas and other marsh plants dominated the well watered lowlands. Sage and juniper were much less common than they are today but they occurred in the same ecological niche, between the conifer forests and the grasslands. This niche was smaller because the cooler, wetter climate created larger wet lands and forests at the expense of the grasslands and juniper/sage steppe. The climate grew warmer and drier as it approached the Holocene and the grasslands and steppe increased at the expense of the forests and wet lands. These changes did not take place at the same time in all locations. Site specific environmental constraints such as aspect, nearness to water, elevation and local weather patterns all influenced the plant communities. An excellent example of this is the relic stand of cedar which exists in a deep, cool, and humid gulch on the north flank of Aldrich Mountain. The next nearest stand of this timber is located over 100 miles to the west. It is thought that during the Pleistocene these trees were fairly common in the Blue Mountains and that this stand survived the drying trend because of it's unique setting.

Although in many basic ways the plant communities of the late Pleistocene are similar to those of today, the animal communities which depended on them were quite different. Particularity distinctive were the large numbers of birds and mammals which went extinct at the end of the Pleistocene and in the early Holocene. These include the giant ground sloth, the giant short-faced bear, the horse, the flat-headed peccary, the camel, the llama, the mammoth, the giant bison, the American lion, the sabertooth cat, the dire wolf, the flamingo, and various storks, condors, vultures, hawks and eagles. Many other small mammals, reptiles, fish and amphibians also probably existed in the late Pleistocene but these have not been described in detail from the fossil record. Most of these animals became extinct by the end of the Pleistocene for reasons which are not well understood. Obviously one factor in the demise of the Pleistocene fauna was the continued warming and drying of the climate and the associated decline in large wet lands and forests. Given that this warming and drying trend happened at different speeds in different locations, and that it seems to have happened fairly slowly, it is hard to believe that more of these animals were not able to adapt to the changes. One explanation which has been put forward is that these animals were driven to extinction by the introduction of a new and deadly predator about 13,000 years ago.