RESEARCH· ·1970·

A.bstmct.-'l'he Curtis Ranch local fauna from near the town
of St. David, Ariz., in the San Pedro valley, contains fossilleporid
mnterinl ussignnl.>le to the genera A.lm·alag1t8 and Lepus. A
new species is described that appears to be related to A.Zurala.g1t·8
bensoncnsis of the Denson local fauna.
The Pliocene a.nd Pleistocene nonmarine sedimentary
sequence in the San Pedro River valley of southern
Arizona (fig. 1) has been the source of a large
number of fossil vertebrate specimens for Inany years.
The fossil assemblages collected there by field parties
v-------------r---
----r-----,
114' 112' 110'
1
I
A
R
0 Prescott
Z 0
oFingstaff
N A
1l'IOURE 1.-Index map of Arizona, showing fossil lagomorph
localities. 11, Benson; B, Curtis Ranch; and o,
Tusker.
GE,OLOGICAL SURVEY RESEARCH 1970
MIDDLE PLEISTOCENE LEPORIDAE FROM
THE SAN PEDRO VALLEY, ARIZONA
By JOE S. DOWNEY, Grand Forks, N. Dak.
from various institutions throughout tli.e United States
have come to be of considerable significance to biostratigraphers
and vertebrate paleontologists working
with Pleistocene faunas ( Gazin, 1942; Hibbard, 1949).
During the past several years these deposits have
yielded a large quantity of fossil material to collectors
from the University of Arizona at Tucson.
Previous studies in the San Pedro valley have dealt
with the physiography and geomorphology (Bryan,
1926; Gilluly, 1956; :Melton, 1960),.yertebrate paleontology
(Gidley, 1922; 19.26; Gazin, 1942; Downey,
1968) , and plant ecology (Zimmermann, 1969) . Zimmermann's
paper contains a recent list of references
to the literature on the geology of the San Pedro
I valley.
Recent work by Gray (1967) in the valley has shown
j that the exposed deposits are a continuous succession of
lacustrine and fluviatile sediments deposited by a large,
I
I low-velocity stream that spread the sediments upon an
aggrading flood plain. The vertebrate fauna collected
I from the sediments suggests that a savanna-grasslands
I
environment existed in the San Pedro valley during
the period of deposition.
I This succession of fine-grained sediments--composed
I
I mainly of silt, clay, fine sand, and fresh-water limestone
with minor interbedded pyroclastic units-constitutes
a distinct lithologic unit, ·and the na.me St.
l
I
I David Formation was proposed by Gray (1967). His
work also indicated that the known fossil-producing
sites in the San Pedro valley are near the top of the
sedimentary sequence.
Two general areas, both near the south end of the
San Pedro valley, have been particularly productive
in regard to fossil material, and the one near the town
of St. David, Ariz., is the source of the fossil specimens
described in this report.
This locality, termed the Curtis Ranch locality by
Gazin (1942) is on the east side of the valley and ap-
U.S. GEOL. SURVEY PROF. PAPER 70D-B, PAGES B131-Bl36
Bl31