is very similar
to the material used by the Moquis in whitening their houses. 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. Undoubtedly they belong to a more recent
period than the rude stone structures described before. Most of the
ancient remains of the Sierra are remnants of tribes that expanded
here from the lowlands, and only in comparatively recent times have
disappeared. I also perceived that they were built by a tribe of
Indians different from those which erected the houses in the caves of
the eastern and northern Sierra Madre, and in the country east of it,
and may safely be ascribed to Opatas.

In spite of the rest here, the animals did not seem to improve on the
grama and buffalo grass. It was rather perplexing to note that they
grew weaker and weaker. The grass of the sierra, which was now gray,
did not seem to contain much nourishment, and it became evident that
the sooner we proceeded on our journey, the better. To save them as
much as possible, we loaded only half the regular weight on the mules
and donkeys, and sent them back the next day to fetch the balance of
the baggage. In this way, and by strengthening the poor beasts with
a judicious use of corn, I managed to pull through and overcome this
most serious of all difficulties, which, at one time, threatened to
paralyse the entire expedition.

On December 31st we moved up a steep zigzag trail cut out by us,
and then went north and east through broken foot-hills. We got into
a series of cordon mesas, but the breaks between them were not at
all difficult to pass. On the mountain sides grew oaks and, higher
up, pines.

The country was wild and rugged. Everywhere we encountered fallen
rocks, and there was a scarcity of water. It was a kind of comfort
to see now and then s