Ancient Irrigation Ditches

this part of its course, averaging about twenty feet in width,
by fifteen to eighteen inches in depth, evidently so built as to
permit the escape of surplus water in event of an unusually
heavy, torrential precipitation. At the end of the 1,700-foot,
straight-away section of the canal, its cross-section becomes
narrower and deeper and, thenceforth, it follows contours
and assumes a meandering course. That it was not intended
to lose water by overflow below that point is further indicated
by the fact the excavated soils and clays were almost uniformly
deposited on the lower side of the canal in places where its
course traverses sloping ground. At one point (E) the canal
turns into the head of what was once a small, shallow ravine,
the course of which was followed to its confluence with an-
other ravine of approximately the same size and length. Im-
mediately below this point of confluence, a heavy fill had been
made-sixty feet long on top with a maximum width of fifty
feet at the base-whence the course of the artificial channel
turned into that of the second ravine, the latter being widened
and deepened to its head.
At another point the canal joins the channel of a much
larger water course of an earlier period, long since ruined by
erosion, drifting and filling so that it is now but a land-locked
slough that is ordinarily dry. With the canal carrying a capa-
city discharge, several acre feet of water must have backed
up the broad bed of this slough, thus, in effect, serving as a
small, temporary storage reservoir (F) the contents of which
would drain back into the canal as soon as the level of the
water therein had been lowered sufficiently. Following the
course of this large ravine for a short distance, it had been
found necessary to construct a straight, narrow and compara-
tively high fill (G) to serve as one bank of the canal and to
prevent the flooding of a depression which would have doubt-
less meant the permanent loss of an appreciable amount of
water.
Along the course of the canal, at distances of several
miles from either end, are several mound-like elevations which
might easily be regarded as being of molian, or wind-blown
origin. Two of these which have been under cultivation for
many years, however, contain chipped chert and flint, clam
and mussel shells, calcined bones, potsherds, bits of changed
wood and other vestigia of human occupancy. That each of

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