135 
Through Kenzin, Pronto, Aden, Chappel, and Dona sidings lava 
fields are in sight in every direction, especially on the south side of the 
railroad; most of them are recent outflows of scoriaceous basalt, but 
some are rhyolite of Tertiary age. 
Aden Crater, 4 miles south of Pronto siding and 7% miles southeast 
of Aden siding, is a cone of lava undoubtedly marking the vent from 
which came one of the large recent lava flows skirted by the railroad in 
this vicinity. In its top is a deep blowhole or steam vent in the lava, 
in which many animal skeletons have been found, including coyotes, 
bobcats, and other animals of the present feiubie; and a remarkable 
ground sloth which Lull’ has identified as Nothrotherium shastense. 
The remains were partly buried in bat guano in a sloping chamber 
about 100 feet below the surface. The bones of the sloth were held by 
the original ligaments and tendons, and some of the periosteum, 
patches of skin, muscle fibers, and claws remain. Most of the hide 
had been devoured by fellow victims, whose teeth marks are visible 
on the remaining fragments. The sloth and other animals had 
evidently fallen into this hole, which is a natural trap in the crater 
rim. The time was many thousands of years ago, for the sloth is of a 
species found also in the Rancho la Brea asphalt in Los Angeles 
where it occurs with bones of middle Pleistocene age. (See pl. 19, B. ) 
Just south of Aden is a prominent knob of rhyolite of the older 
volcanic series with a basalt flow at its foot, and 3 miles west are other 
SOUTHERN PACIFIC LINES 
and in large part removed or cut back 
by erosion. They were erupted from 
cracks or craters, some of which are still 
izable by 
® Along or near the railroad in 
the D., grained, 
xas, are the product of | is mostly of light color, and consists 
eruptions that continued for a large | mainly of ash and small grains of 
part of Tertiary time. They consist | pumice. It was blown out of vents by 
of alternating lava flows of various | steam and deposited by wind or water 
kinds, mainly of the varieties known as | in great sheets over the lava flows or 
rhyolite, andesite, and latite, which | other surfaces; in most places it was 
differ in character and order from | covered by later lava flows, the erup- 
place to place and are locally separa: tions generally consisting of alterna- 
by thick beds of light-colored tuff and 
volcanic ash. These lavas and beds 
of fragmental materials occur in sheets 
of varying thickness; some of them are 
several hundred feet thick and of wide 
They are much older than the 
ent, for they have been uplifted, tilted, 
tions of lava outflows and ejections of 
fragmental materials. There were also 
mud fiows, consisting of material 
similar to the tuff and ash, mixed with 
water, which poured out of craters or 
vents and spread over the surface in 
plastic condition, in places to a thick- 
ness of 50 feet or more. 
1 Lull, R. S., A remar 
sloth: Yale Univ: Peabody Mus. ik, 
vol. 3, pt. 2, 1929. 
