The stones themselves were felsite, which abounds in the locality.

The blocks have an average size of twelve inches square by six inches thick.

It should be noted that no regard was paid to the tying of the corners and the partition walls; but considerable care had been taken in making the walls vertical, and the angles were fairly true.

The walls were almost twelve inches thick, and on the inner side they had evidently never been plastered.
Being coated with some white plaster, these ruins look white at a distance, and the Mexicans therefore called them _casas blancas_.

I heard of an extensive group of such buildings near Sahuaripa, and there are also some ruins of this category near Granados, and in the hills east of Opoto.