LATE HOLOCENE HISTORY OF THE WALKER RIVER: THE TALE OF A RIVER WITH A SPLIT PERSONALITY

The Walker River is one of five major streams that flow into the Lahontan basin of northwestern Nevada. The behavior of this river is unusual because instead of flowing into Walker Lake as it does today, at times during the Holocene it diverted into a paleochannel to flow to the Carson Sink. When this happened, Walker Lake lost its major source of water and the Carson Sink gained a significant new source. Paleoclimatic reconstructions based on lake-level fluctuations in both basins must therefore consider the diversion history of the Walker River.

Radiocarbon ages from three study sites along the paleochannel indicate that flow was directed toward the Carson Sink during the time intervals of 1520–1320, 1260–1060, 1070–940, 510–290, and 310–250 cal yr B.P. Because of the overlapping nature of some of these calibrated ages, it is possible that the same diversion event is recorded at more than one site.

Five late Holocene highstands have occurred at Walker Lake since about 3500 cal yr B.P. Three of the regressions from these highstand events are approximately coeval with periods of flow through the paleochannel and into the Carson Sink. During the period from about 1300–900 cal yr B.P. lake levels were relatively low at Walker Lake but flow was occurring, for at least part of this period, in the paleochannel.

In the Carson Sink, relatively large lakes were present during the periods 1520–1310 and at about 900–800 cal yr B.P., respectively. The timing of both of these Carson Sink highstands is consistent with the timing of flow through the paleochannel and major regressions or low water periods at Walker Lake. Simple paleohydrologic modeling suggests, however, that the addition of the Walker River—under modern flow conditions—is not enough by itself to increase lake levels to those documented for the late Holocene. The Humboldt River is suspected in playing a major role for these highstands.

Results from this study are beginning to form a coherent picture of the paleohydrologic history of this complex system. More work needs to be done, however, on the causes of the diversions and on separating the diversion signal from the paleoclimatic signal.