[Illustration:  Pyramid Peak and Lake of the Woods, near Lake Tahoe, Calif.]

[Illustration:  Snow Bank, Desolation Valley, near Lake Tahoe]

[Illustration:  Grass Lake, near Glen Alpine Springs]

Truckee Canyon and Donner Lake Glaciers.  I have said that one of the outlets of the great “mer de glace” was by the Truckee River Canyon.  The stage road to Lake Tahoe runs in this canyon for fifteen miles.  In most parts of the canyon the rocks are volcanic and crumbling, and therefore ill adapted to retain glacial marks; yet in some places where the rock is harder these marks are unmistakable.  On my way to and from Lake Tahoe, I observed that the Truckee Canyon glacier was joined at the town of Truckee by a short but powerful tributary, which, taking its rise in an immense rocky amphitheater surrounding the head of Donner Lake, flowed eastward.  Donner Lake, which occupies the lower portion of this amphitheater, was evidently formed by the down-flowing of the ice from the steep slopes of the upper portion near the summit.  The stage road from Truckee to the summit runs along the base of a moraine close by the margin of the lake on one side, while on the other side, along the apparently almost perpendicular rocky face of the amphitheater, 1000 feet above the surface of the lake, the Central Pacific Railroad winds its fearful way to the same place.  In the upper portion of this amphitheater large patches of snow still remain unmelted during the summer.

    My examination of these two glaciers, however, was very
    cursory.  I hasten on, therefore, to others which I traced more
    carefully.

Lake Tahoe lies countersunk on the very top of the Sierra.  This great range is here divided into two summit ridges, between which lies a trough 50 miles long, 20 miles wide, and 3000 to 3500 feet deep.  This trough is Lake Valley.  Its lower half is filled with the waters of Lake Tahoe.  The area of this Lake is about 250 square miles, its depth 1640 feet, and its altitude 6200 feet.  It is certain that during the fullness of glacial times this trough was a great “mer de glace,” receiving tributaries from all directions except the north.  But as the Glacial Period waned—­as the great “mer de glace” dwindled and melted away, and the lake basin became occupied by water instead, the tributaries still remained as separate glaciers flowing into the Lake.  The tracks of these lingering small glaciers are far more easily traced and their records more easily read, than those of the greater but more ancient glacier of which they were once but the tributaries.

Of the two summit ridges mentioned above the western is the higher.  It bears the most snow now, and in glacial times gave origin to the grandest glaciers.  Again:  the peaks on both these summits rise higher and higher as we go toward the upper or southern end of the Lake.  Hence the largest glaciers ran into