March 2021 • Nebraskaland 47
plants were just coming into their own. The North American
Western Interior Seaway covered much of the continent. The
sea stretched from the Rocky Mountains to eastern Nebraska,
and from the Arctic Ocean to the Gulf of Mexico.
The sea fl uctuated in depth and extent, covering eastern
Nebraska with deep to shallow water or coastal vegetation.
"The best analogy of what Nebraska was like when the
Dakota's sediments were deposited is the present-day coastal
plain of Louisiana," Diff endal said. "Think of a low fl oodplain
forest with low relief close to the ocean."
Rivers fl owing westward to the sea deposited sands into
river channels and estuaries where the streams met the
sea, while depositing lighter clays into quiet fl oodplain
backwaters and tidal marshes. Imperceptibly slow and over
a vastness of time, the Dakota's sediments accumulated to
great thickness. Later, the sea deepened, and the Dakota
was covered by water-deposited lime and clay sediments
and, when the sea fi nally receded, by upland sediments.
Now, deeply buried, the Dakota's sands were compacted and
weakly cemented into soft, white to rusty-red sandstone and
the clays into yellow, pinkish and other pastel-colored shale.
Relatively recently in geological history, the overlying
sediments eroded away, exposing the Dakota on the land
surface. This sandstone exposure extends from southern
Jeff erson County through central Kansas and into Oklahoma.
In northern Nebraska, the Dakota remains buried, except
for small outcroppings mainly on river bluff s, making the
Jeff erson County landscape unique for Nebraska.
Grinding Glacial Ice
Scattered among Rock Glen's prairies and woods are
variously-colored boulders, some the size of refrigerators.
Diff endal identifi ed them as quartzites, granites, schists and
Rock Glen Wildlife Management Area is nestled in the hills of southern Jeff erson County, one of eastern Nebraska's few
remaining native landscapes. Native prairie covers the hills while bur oak woods fi ll the ravines.
PHOTO
BY
ERIC
FOWLER
