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Show XXII ANNUAL REPORT OF THE DIRECTOR Valley Range. To the east of these peaks, stretching far beyond the present channel of the Rio Grande, there was once a great Tertiary lake, which was gradually filled with the sands washed into it on every hand and by the ashes blown out of the adjacent volcanoes. This great lake formation is in some places a thousand feet in thickness. When the lake was filled the Rio Grande cut its channel through the midst to a depth of many hundreds of feet. The volcanic mountains to the westward send to the Rio Grande a number of minor streams, which in a general way are parallel with one another. The Rio Grande itself, and all of these lateral streams, have cut deep gorges and canyons, so that there are long, irregular table- lands, or mesas, extending from the Rio Grande back to the Valley Mountains, each mesa being severed from the adjacent one by a canyon or canyon valley; and each of these long mesas rises with a precipitous cliff from the valley below. The cliffs themselves are built of volcanic sands and ashes, and many of the strata are exceedingly light and friable. The specific gravity of some of these rocks is so low that they will float on water. Into the faces of these cliffs, in the friable and easily worked rock, many chambers have been excavated; for mile after mile the cliffs are studded with them, so that altogether there are many thousands. Sometimes a chamber or series of chambers is entered from a terrace, but usually they were excavated many feet above any landing or terrace below, so that they could be reached only by ladders. In other places artificial terraces were built by constructing retaining walls and filling the interior next to the cliff with loose rock and sand. Very often steps were cut into the face of a cliff and a rude stairway formed by which chambers could be reached. The chambers were very irregularly arranged and very irregular in size and structure. In many cases there is a central chamber, which seems to have been a general living room for the people, back of which two, three, or more chambers somewhat smaller are found. The chambers occupied by one family are sometimes connected with those occupied by another family, so that two or three or four sets of chambers have interior communication. Usually, however, the communication from one system of |
