The lower ruin covers an area of about 150 by 50 feet, raised but a few feet above the bottom land, probably by its own debris. Within this area there are remains of 45 rooms on the ground, in addition to a circular kiva. On the east side there are walls still standing to a height of 12 and 14 feet. It is probable that the lower ruin comprised about 60 rooms, which, with a liberal allowance for the rooms in the cave, would make a total of 80. This would furnish accommodations for a maximum of 10 or 12 families or a total population of 50 or 60 persons. It is probable, however, that this estimate is excessive and that the total population at any one time did not exceed 30 or 40 persons. [Illustration: Fig. 14--Ground plan of the lower part of Casa Blanca ruin.] The ground plans shown are the result of a very careful survey, plotted on the ground on a large scale (10 feet to 1 inch--1:120), and the irregularities shown were carefully noted and put down at the time. These irregularities, which are commonly ignored in the preparation of plans of ruins, are of the highest importance. From them the sequence of construction can often be determined. [Illustration: Fig. 15--Ground plan of the upper part of Casa Blanca ruin.] The walls of the lower ruin are somewhat obscured by loose debris, of which a large amount is lying about. Roof debris is especially abundant; it consists of small twigs and lumps of clay, with ends of beams projecting here and there. The principal walls occur in the eastern part, where some of them are 2 feet thick and still standing to a height of 10 and 12 and in one place of 14 feet. An inspection of the plan will show that, as is invariably the case where a wall rises to a height of more than one story, the lower part is massive and the upper wall sets back 5 or 6 inches, reducing its thickness by that amount. All the heavy walls occur either about the kiva or east of it. Apparently these walls were built first especially heavy and massive, and afterward, when upper stories were added, it was not found necessary to carry them up the full thickness. It will be noticed that the wall extending eastward from the corner of the kiva, and which is from a foot to 6 feet high at the present time, extends through the heavy wall which crosses it 33 feet to the east, and is continuous to its termination about 50 feet east, against another heavy wall. The last-mentioned wall is also continuous from the cliff out to the front of the ruin, a distance of about 46 feet.