270 BOTANICAL GAZETTE [APRIL 
even flattened cones, though the second highest peak, Mt. Rose 
(10,800 feet), has a steep ascent to the top. Its much more gentle 
contours are no doubt due to receiving far less rainfall than the 
Divide, and to the erosional force being consequently many times less. 
Between these limiting ranges the drainage all centers in the 
Truckee River. The Upper Truckee rises north of Round Top, 
enters Lake Tahoe east of Tallac and, as the Truckee River, 
emerges from the northwest corner of the lake. Its course is 
north to the point of union with Donner Creek and then northeast 
through the Truckee Canon to the floodplains about Reno, Ne- 
vada. All of its important tributaries enter from the west, having 
their sources in the Divide’s many lakelets. 
These alpine and subalpine tarns are among the greatest charms 
of the region. They commonly fill the glacial cirques and often 
form a series of small basins from whose lowest margin the con- 
necting brook cascades to the major stream. These pools are being 
gradually silted up both by sediment washed in from the adjacent 
slopes and by the vegetation fringing the banks; in time they be- 
come marshes and finally meadows, which in turn yields to the 
forest, for, as shown below, the forest is in this region of the Sierra 
the ultimate phase, since the elevation is not great enough to cause 
a cold timber line. On the broad ridge between Gilmore Lake and 
Suzy Lake above Glen Alpine is such a series of nearly filled basins, 
the largest of which is already converted into a marshy meadow, 
on whose margin a young growth of lodge pole pine has started. 
As these lakes are mainly in glacial basins, they are frequently 
banked on the low side by moraines, which in places become Of 
major importance in the local topography. The glaciers of the 
region have formed large deposits as lateral and terminal moraines 
about Independence and Donner Lakes, and on the west shore ol 
Lake Tahoe an ancient extension of the last has been cut off by 
several terminal moraines of the Fallen Leaf Glacier and now 
persists as a separate lake, three miles long. The moraines on the 
sides of this lake are especially large, the eastern one being as long 
as the lake and goo feet high. 
Some of the valleys through which the larger glaciers moved 
have the U-shaped cross-section characteristic of glaciated moun- 
