Many artificial reservoirs dating to prehistoric times were observed in
the area covered by the author’s reconnoissance. These fall into two
well-marked types, one form being a circular depression, apparently
excavated and sometimes walled up with earth or stones. The other
form was not excavated by man, but the sloping surface of rock was
surrounded on the lowest level by a bank of earth, forming a dam or
retaining wall. Both types of reservoirs are commonly formed near some
former center of population, but sometimes occur far from mounds,
wherever the surface of the land has a convenient slope and the water
can be compounded by a retaining wall. The height of the bank that
holds back the water of these prehistoric reservoirs has been increased
in some cases by stockmen; the walls of others still remain practically
the same height they were when constructed by the aborigines. One of
the best examples of the second type of reservoir, the retaining wall
of which is shown in plate 32, _a_, is crossed by the road to Bluff
City near the ruins in Holly Canyon, not far from Picket corral. A few
miles north of this reservoir, at the edge of the cedars, the road
crosses another of these ancient reservoirs, whose retaining bank
has been considerably increased in height by stockmen. The ancient
reservoir at Bug Mesa covers fully 4 acres, and the reservoir near
Goodman Point Ruin is almost as large, and, although somewhat changed
from its aboriginal condition, is still used by farmers dwelling in the
neighborhood. The latter belongs to the first type; the former to the
second. Reservoirs of one or the other type are generally found in the
neighborhood of all large heaps of rocks, the so-called mounds that
indicate the former existence of pueblos. The reservoir of the Mummy
Lake village on the Mesa Verde belongs to the excavated type.