Extent of Pleistocene Lakes in the Western Great Basin

The purpose of this map is to show the differences between the extents of late
Pleistocene pluvial lakes and older, larger lakes caused by much higher
effective moisture during past glacial-pluvial episodes.

During the Pliocene to middle Pleistocene, pluvial lakes in the western Great
Basin repeatedly rose to levels much higher than those of the well-documented
late Pleistocene pluvial lakes, and some presently isolated basins were
connected. Sedimentologic, geomorphic, and chronologic evidence at sites shown
on the map indicates that Lakes Lahontan and Columbus-Rennie were as much as 70
m higher in the early-middle Pleistocene than during their late Pleistocene
high stands. Lake Lahontan at its 1400-m shoreline level would submerge
present-day Reno, Carson City, and Battle Mountain, and would flood other
now-dry basins. To the east, Lakes Jonathan (new name), Diamond, Newark, and
Hubbs also reached high stands during the early-middle(?) Pleistocene that were
25-40 m above their late Pleistocene shorelines; at these very high levels, the
lakes became temporarily or permanently tributary to the Humboldt River and
hence to Lake Lahontan. Such a temporary connection could have permitted fish
to migrate from the Humboldt River southward into the presently isolated Newark
Valley and from Lake Lahontan into Fairview Valley. The timing of drainage
integration also provides suggested maximum ages for fish to populate the
basins of Lake Diamond and Lake Jonathan. Reconstructing and dating these lake
levels also has important implications for paleoclimate, tectonics, and
drainage evolution in the western Great Basin. For example, shorelines in
several basins form a stair-step sequence downward with time from the highest
levels, thought to have formed at about 650 ka, to the lowest, formed during
the late Pleistocene. This descending sequence indicates progressive drying of
pluvial periods, possibly caused by uplift of the Sierra Nevada and other
western ranges relative to the western Great Basin. However, these effects
cannot account for the extremely high lake levels during the early middle
Pleistocene; rather, these high levels were probably due to a combination of
increased effective moisture and changes in the size of the Lahontan drainage
basin.