RESEARCH· ·1970·

B148
5
10
15
20
X
X
Plntygonus
Pla.tygon'll.~
10.3 ft
iii
~
c
0
:;;
Cll
"tl
c
:J
0
u..
2l~ftl ____________ _
Reddish-brown silty sand;
threadlike concentrations of
CaC0 3
Light-brown fine
eolian sand
Broadway
25 Alluvium
25.7 ft ,------:-----:-----:-----
_:::::::,._ _ _; Brown1sh-gray laminated s1lty '-
clay; pebbles as much as 1
inch in size; wet; moderate
27~~--~~~rati~~CaCOJ ___
30
Moderate- yellowish- brown
clayey coarse sand; occasion-
29~~--~~bbl:.:._ ______ _
Clean free-running yellowishbrown
coarse sand
FIGURE 10.-Cross-sectional columnar section of eolian sand
and Broadway Alluvium at Juvenile Hall. Section measured
June 6, 1967, by G. R. Scott, R. l\1. Lindvall, .and R. W.
O'Donnell.
part possibly is an overbank late flood deposit such as
is observed on most terraces near Denver. The other
three lithologies are typical of Broadway Alluvium
?
STRATIGRAPHY
and demonstrate conclusively that the eolian sand at
Juvenile Hall deeply covers the Broadway terrace.
The eolian sand, shown in cross section in figure 10,
is composed of light-brown, fine, well-sorted, slightly
rounded sand. Generally, either it is not stratified or
it ~hows the sweeping curves of cross-stratification that
characterize most sand dunes. Most of the sand is uncemented
and only slightly consolidated, but in the
upper part it is slightly to firmly cemented by secondary
clay and calcium carbonate as a result of soil formation.
It is 22 feet thick at Juvenile Hall (fig. 10),
but may be twice as thick at other places. A moderately
well developed Altithermal soil is formed in the upper
part of the eolian sand.
The eolian sand was blown chiefly out of the valley
of the South Platte River. Strong winds from the
northwest deflated alluvium in the valley and possibly
also carried away silt from outcrops of loose Denver
Formation and deposited the sand and silt many miles
down wind. Lack of vegetation on the newly deposited
outwash of the Broadway Alluvium of Pinedale age
made the fine part of the outwash readily available to
wind erosion. In general, eolian sand lies immediately
downwind and loess farther downwind from the valley.
Peccary is one of the few fossils found in the eolian
sand in the. Denver area. Ages assigned to Platygonus
compresstts are Sangamon (Schultz and others, 1951,
table 1; Hibbard and Taylor, 1960, p. 27 and 32;
Slaughter and Ritchie, 1963, p. 126, 128) and Wisconsin
(Hibbard, 1958, table 1).
The eolian sand has previously been called late Wisconsin
and early Holocene in age (Hunt, 1954, p. 112-
113; Scott, 1962, p. 32; Scott, 1963, p. 41). We believe
that it was deposited starting in Pinedale time and
ending when the "Altithermal" soil was formed about
4,500 years ago.
REFERENCES
Carr, W. J., and Trimble, D. E., 1963, Geology of the American
Falls quadrangle, Idaho: U.S. Geol. Survey Bull. 1121-G,
44 p.
Cheatum, E. P., and Allen, Don, 1963, An ecological comparison
of the Ben Franklin and Clear Creek local molluscan
faunas in Texas: Graduate Research Center Jour., v. 31,
no. 3, p. 174-179, 1 table.
Gardner, M. E., 1967, Quaternary and engineering geology of
the Orchard, Weldona, and Fort Morgan quadrangles,
Morgan County, Colorado: Colorado School Mines Ph. D.
thesis, 283 p.
Hibbard, C. W., 1955, The Jinglebob interglacial ( Sangamon?)
fauna from Kansas and its climatic significance: Michigan
Univ. Mus. Paleontology Contr., v. 12, no. 10, p. 170-228,
2 pls., 8 figs., 1 chart.
-- 1958, Summary of North American Pleistocene mammalian
local faunas: Michigan Acad. Sci., Arts, and Letters
Papers, v. 43, p. 3-32, 1 table.