RESEARCH· ·1970·

GE,OLOGICAL SURVEY RESEA·RCH 1970
GEOLOGY OF NEW OCCURRENCES OF PLEISTOCENE BISONS
AND PECCARIES IN COLORADO
By GLENN R. SCOTT and ROBERT M. LINDY ALL,
Denver, Colo.
A.bstt·aot.-New occurrences of Quaternary mammals in Colorado,
including Bison ( G-irJantolJison) la,ti.ft·ons in Slocum Alluvium
of Snngnmon nge; B'ison (Shnob1son) P alleniP in Louviers
Alluvium of enrly Bull T.Jnke age; nnd Platygon1t8 cotnpt·essus
in eolinn snnd of Pineclnle and early Holocene age, permit a
more definite assignment of age to these vertebrate species
thnn hns been possible in the pnst.
Two new occurrences of Pleistocene bison, Bison
(-Gigantobison) latif'rons and Bison (Simobison) ?
alleni.~, and one of peccary, Platygonus compressus,
are stratigraphically well documented and permit a
more definite assignment of age to these vertebrate
species than has been possible in the past. All occur
in deposits that are part of a well-established Quaternary
sequence along the Rocky l\1ountains front (Scott,
1960).
'"!''his sequence of deposits consists of alluvium on a
series of pediments and terraces that range in elevation
from nearly 500 feet above present stream level for the
oldest to only a :few feet above stream level for the
youngest. Differences in degree of weathering and soil
profiles imposed on the deposits, as well as in height
above stream level, ~tre useful in determining stratigraphic
position. The deposits, their ages, and their
heights above modern 'Streams ~we fr01n oldest Ito youngest:
Nussbaum Alluvium of Pleistocene age, 470 feet;
Rocky Flnts Alluvium of Nebraskan or Aftonian age,
360 feet; Verdos Alluvium of J(ansan or Yarmouth
age, two levels ttt 220 feet and 290 feet (a level intermediate
between Rocky Flats and typical Verdos) ;
Slocmn Alluvium of Illinoian or Sangamon age, two
levels at 120 feet and 180 feet (a level intermediate
between Verdos nnd typical Slocmn); Louviers Alluvium
of Bull Lake age, 80 feet; Broadway Alluvium
of Pinedale age, 40 feet; and Piney Creek Alluvium
and post-Piney Creek alluvium of late Holocene age,
respectively 25 and 5 feet ( nnd the flood plain) .
GIANT BISON FROM CANON CITY
A horn core on display in the municipal museum in
Canon City, Colo., was recognized as that of a giant
bison by Scott in July 1967. This horn core, which had
been found near Canon City a year earlier (fig. 1),
was identified by G. Edward Lewis as Bison ( Gigantobison)
latif'rons Harlan and was described by him
(Lewi's, 1970) (p. B137, tJhis chapter).
The horn core is from a skull found in gravel about
5 feet above the floor of a pit leased by the Fremont
County Highway Department in sec. 26, T. 18 S., R. 70
"V., Fremont County, Colo. This gravel is part of the
Slocum Alluvium along Fourmile Creek, a tributary
of the Arkansas River near Canon City. The Slocum
Alluvium here consists chiefly of 11-25 feet of yellowish-red
well-stratified gravel that contains pebbles,
cobbles, and boulders generally in lenses (fig. 2).
Large lumps and layers of olive-gray shale reworked
from the underlying Pierre Shale are abundant. The
gravel is cross-stratified in. a manner typical of stream
deposits; it also contains channels filled with coarse
gravel. The upper part of the Slocum Alluvium consists
of about 4 feet of clayey pebbly sand and silt that
conformably overlies the lower part. This division of
the Slocum into a thick gravel and a thin overlying
pebbly sand and silt is typical of the Slocum and of
most pediment alluvium. The Slocum, except for the
lower bouldery part, is slightly cemented by clay
throughout and by calcium carbonate in the upper
part where a pre-Bull Lake soil is developed; the lower
bouldery part of the gravel is uncemented.
Near Canon City, ·alluvium in two terraces at 120
and 180 feet above the Arkansas River is placed in the
lJ.S. GEOL. SURVEY PROF. PAPER 70G-B, PA:GES Bl41-Bl49
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