26

uplift, the streams had fairly high gradients and much of the eroded material
was transported out of the region, fresh supplies of the country rock being
constantly added to the stream deposits.

PLEISTOCENE AND RECENT

The unconsolidated deposits overlying the bedrock consist of Recent
(post-Glacial) alluvium, glacial drift formed during the Ice Age immediately
preceding the present period, interglacial deposits formed during one or
more periods of temporary retreat of the ice during the Pleistocene or
Glacial period, and gold-bearing gravels, parts of which are pre-Glacial in
age.

The Recent deposits have been formed mainly by streams eroding the
drift deposits and, to some extent, the bedrock. They consist of sands,
gravels, silt, and muck or peat deposited in the beds and on the flood-plains
and terraces of the present streams. The deposits on the lower terraces of
the streams are partly late Glacial and partly Recent, there being no sharp
dividing line between the two sets of deposits. The glaciers probably
retreated from the region only 10,000 or 15,000 years ago and a small
remnant of one of them still remains in the cirque basin on the north side of
mount Agnes. The Recent deposits as a rule are only 10 or 15 feet thick,
and in the lower part of Williams creek and at other places include fairly
large amounts of tailings from hydraulic mines. The tailings in Williams
creek are said to average about 25 feet in thickness. In the part above the
town of Barkerville and below the canyon there is probablya filling of nearly
40 feet, judging by old photographs of the creek. There are also heavy
fillings of tailings at the mouths of Lowhee and Grouse creeks.

Glacial drift is abundant in the area, and in places fills the valley
bottoms to a considerable depth, the greatest thickness known being in the
valley of Slough creek opposite the mouth of Nelson creek, where borings
have shown the surface deposits to have a maximum thickness of 287 feet.
In many places the drift mantles the sides of the valleys up to more than
1,000 feet above the valley floors and, in some places—as on Proserpine
mountain—boulder clay occurs at an altitude of 5,500 feet. At higher
altitudes it is mostly thin or is absent, but erratics occur on some of the
highest summits—for example on mount Murray and mount Agnes—at
altitudes of nearly 6,500 feet. The glacial drift in the valleys is nearly all of
local origin, though foreign boulders occur. For example, large boulders of
conglomerate and numerous pebbles and stones of red argillite, which must
have been derived from the mountain ridge on the northeast side of Little
Valley and Pleasant Valley creeks, are fairly abundant in the upper part of
Williams creek and at other places several miles to the southwest of the
mountain ridge.

Glacial strie are well developed at only a few places in the area. They
are particularly distinct on both sides of Williams creek a short distance
above the canyon between Barkerville and the old town of Richfield, and
on the upper part of Cunningham creek, where a considerable area of
bedrock, glacially striated and grooved, has been exposed by mining.
Strie on the uplands were noted at only one place—Bald mountain. In
the valleys they all trend downstream and were, therefore, probably formed