surface, as a deep excavation in fairly even ground would naturally be made in a straight line.
Plate XXXVIII. Bluff Over Ancient Ditch, Showing Gravel Stratum.
The face of the bluff shows an even deposit of sand, without apparent stratification, except here and there a thin layer or facing of mud occurs, such as covers the bottom of the ancient ditch and also of the modern ditch. Singularly enough, however, over the ancient ditch, about 5 feet above its bottom, there is a stratum of sand and gravel, and on top, within a few inches of the surface of the ground, a thin stratum of mud. This mud stratum extends only about 8 feet horizontally and is slightly hollowed, with its lowest part over the center of the ditch. The gravel stratum also was laid down over the ditch, is tilted slightly southward and occurs in two layers, together about a foot thick. It first appears a few feet south of the point where the main ditch enters the bluff and over the ditch both layers are distinctly marked, as shown in plate XXXVIII. Both layers are clearly marked to a distance of 4 feet north of the northern side of the main ditch; here the lower layer thins out, but the upper layer continues faintly marked almost to the edge of the small ditch. At this point the gravel stratum becomes pronounced again and continues over the small ditch, almost pure gravel in places, with a decided dip westward. At a point just beyond the northern side of the small ditch the gravel layer disappears entirely.
The occurrence of this gravel in the way described seems to indicate that the ditch was built along the slope of a low hill forming the edge of the bottom land at that time, and that subsequently detritus was deposited above it and over the adjacent bottom land forming a smooth ground surface. Against this hypothesis it must be stated that no evidence whatever was found of more than a single deposit of sandy loam, although the exposures are good; but perhaps were an examination made by a competent geologist some such evidence might be developed.
There is one fact that should not be lost sight of in the discussion, viz, the very low elevation of the ditch above the river. The Verde is, as already stated, a typical mountain stream, with an exceptionally high declivity, and consequently it is rapidly lowering its bed. If, as already conjectured, the water for the ancient ditch was taken from the river but a short distance above the point where remains of the ditch are now found—and this assumption seems well supported by the character of the adjacent topography—the slight elevation of the bed of the ditch above the river would indicate that, in the first place, the ditch was located, as already suggested, along the slope of a hill, and in the second place, that the ditch was built at a period of no great antiquity. The occurrence of the high bluff under which the ditch now passes does not conflict with this suggestion, for the deposition of the material composing it and its erosion into its present form and condition may be the result of decades rather than of centuries of work by
a stream like the Verde, and certainly a hundred, or at most a hundred and fifty years would suffice to accomplish it. At the present time a few floods deposit an amount of material equal to that under discussion, and if subsequently the river changed its channel, as it does at a dozen different points every spring, a few decades only would be required to cover the surface with grass and bushes, and in short, to form a bottom land similar to that now existing over the ancient ditch.
In conclusion it should be noted, in support of the hypothesis that the ditch was built before the material composing the bluff was laid down, that immediately under the ditch there is a stratum of hard adobe-like earth, quite different from the sand above it and from the material of which the bluff is composed. This stratum is shown clearly in [plate XXXVIII].
The hypothesis which accords best with the evidence now in hand is that which assumes that the ditch was taken out of the river but a short distance above the point illustrated, and that it was built on the slope of a low hill, or on a nearly flat undulating bottom land, before the material composing the present bottom or river terrace was deposited, and that the ditch, while it may be of considerable antiquity, is not necessarily more than a hundred or a hundred and fifty years old; in other words, we may reach a fairly definite determination of its minimum but not of its maximum antiquity.