[Illustration: Figure 44. _The last inch of the yardstick, enlarged
to show subdivisions of the Cenozoic Era._]
STRATIGRAPHIC SCALE THE LAST INCH OF ABSOLUTE TIME (million
THE YARDSTICK years ago)
CENOZOIC
QUATERNARY
Recent and 0 0
Pleistocene
TERTIARY
Pliocene 0 0
Miocene ⅛ 12
Oligocene ¼ 25
Eocene ⅜ 40
Paleocene ⁷/₁₆ 55
MESOZOIC
CRETACEOUS ½ 65
The Cenozoic (table 1), last and shortest of the geologic eras,
comprises the Tertiary and Quaternary Periods. It began about 65 million
years ago and is represented by only the final one-half inch of our
imaginary yardstick of time (fig. 19). Nevertheless, it is the era
during which the Tetons rose in their present form and the landscape was
sculptured into the panorama of beauty that we now see. In order to show
the many Tertiary and Quaternary events in the Teton region, it is
necessary to enlarge greatly the last part of the yardstick (fig. 44).
There are two reasons for the extraordinarily clear and complete record.
First, the Teton region was a relatively active part of the earth’s
crust, characterized by many downdropped blocks. The number of events is
great and their records are preserved in sediments trapped in the
subsiding basins. Second, the geologically recent past is much easier to
see than the far dimmer, distant past; the rocks that record later
events are fresher, less altered, more complete, and more easily
interpreted than are those that tell us of older events.
[Illustration: Table 5.—Cenozoic sedimentary rocks and
unconsolidated deposits in the Teton region.]
Age Formation Thickness Description Where exposed
(feet)
QUATERNARY
Recent
Modern 0-200± Sand, gravel, and Floor of Jackson
stream, silt along present Hole and in canyons
landslide, streams; jumbled and on
glacial and broken rock in mountainsides
talus deposits landslides and on throughout the
talus slopes; region.
debris around
existing glaciers.
Pleistocene
Glacial 0-200± Gravel, sand, silt, Floor of Jackson
deposits and and glacial debris. Hole.
loess
Unnamed upper 0-500 Shale, brown-gray, Gros Ventre River
lake sequence sandstone, and Valley.
conglomerate.
Unnamed lower 0-200 Shale, siltstone, National Elk Refuge.
lake sequence and sandstone,
gray, green, and
red.
? Pleistocene or Pliocene
Bivouac 0-1,000 Conglomerate, with Signal Mountain and
Formation purplish-gray West Gros Ventre
welded tuff in Butte.
upper part.
TERTIARY
Pliocene
Teewinot 0-6,000 Limestone, tuff, National Elk
Formation and claystone, Refuge, Blacktail
white, soft. Butte, and eastern
margin of Antelope
Flat.
Camp Davis 0-5,500 Conglomerate, red Southernmost tip of
Formation and gray, with Jackson Hole.
white tuff,
diatomite, and red
and white claystone.
Miocene
Colter 0-7,000 Volcanic Pilgrim and Ditch
Formation conglomerate, tuff, Creeks, and north
and sandstone, end of Teton Range.
white to
green-brown, with
locally-derived
basalt and andesite
rock fragments.
Oligocene
Wiggins 0-3,000 Volcanic Eastern margin of
Formation conglomerate, gray Jackson Hole.
to brown, with
white tuff layers.
Eocene
Unnamed upper 0-1,000 Tuff, conglomerate, Eastern margin of
and middle sandstone, and Jackson Hole.
Eocene claystone, green,
sequence underlain by
variegated
claystone and
quartzite pebble
conglomerate.
Wind River 2,000-3,000 Claystone and Eastern margin of
and Indian sandstone, Jackson Hole.
Meadows variegated, and
Formations locally-derived
conglomerate;
persistent coal and
gray shale zone in
middle.
Paleocene
Unnamed 1,000-2,000 Sandstone and Eastern margin of
greenish-gray claystone, Jackson Hole.
and brown greenish-gray and
sandstone and brown,
claystone intertonguing at
sequence base with quartzite
pebble conglomerate.
Pinyon 500-5,000 Conglomerate, Eastern part of
Conglomerate brown, chiefly of Jackson Hole, Mt.
rounded quartzite; Leidy and Pinyon
coal and claystone Peak Highlands, and
locally at base. north end of Teton
Range.
[Illustration: Figure 45. _Pinyon Conglomerate of Paleocene age,
along the northwest margin of the Teton Range._]
During the early part of the Tertiary Period, mountain building and
basin subsidence were the dominant types of crustal movement. Seas
retreated southward down the Mississippi Valley and never again invaded
the Teton area. Environments on the recently uplifted land were diverse
and favorable for the development of new forms of plants and animals.