Geology Reference
In-Depth Information
"The Ship" at The Cove Palisades State Park is composed of tuffaceous Deschutes beds capped
by rimrock basalt. (Photo Oregon State Dept. of Transportation)
areas of eastern Oregon. Layered between the basalts
layers of the Deschutes Formation compose the narrow
are sediments laid down by the river waters that were
neck of the isthmus between the two rivers at the south
impeded by the volcanic debris. Events during this time
end of The Island. The Peninsula is made up of Plio-
are recorded in the canyon walls by rocks on the east
cene and Pleistocene lavas extruded 2 to 3 million years
rim of Lake Simtustus.
ago from local vents. Smaller amounts of lavas covered
After sucessfully cutting through these basalts for
low spots in the valley and diverted the ancient streams
7 million years, the ancient Deschutes river was once
and rivers.
again inundated when Cascade volcanoes began to fill
Once this eruptive activity had ceased, the river
the channel with volcanic debris, ash, and cinders,
could concentrate its energy renewing and deepening its
blocking the waterflow and creating lakes in places.
channel, which followed the same path as it does today.
Mixed in with this volcanic material are silt, sands, and
In a final volcanic event beginning 1.6 million years
gravels carried by the Deschutes as it continued to
ago, hot liquid lava poured into the Crooked River,
work at eroding these new obstructions. Most of the
entering the canyon upriver near O'Neil. This lava,
yellowish-brown sands and black basalts seen in the
from vents at the base of Newberry Volcano, flowed for
canyon walls were produced during this interval from
miles downstream from that point, filling the canyon.
8 million to 4 million years ago. Distinctive ignimbrite
At least 15 separate flows inundated the canyons as far
layers are common between the river sediments and
as Round Butte in the park before coming to a halt.
lavas. Ignimbrites develop when hot air-borne ash falls
After moving such a distance, the lavas had cooled
to cool as a glassy layer. At The Cove Palisades park an
somewhat to become thick and sluggish. In the narrows
ignimbrite comprises the distinctive white prow of "the
here, a dam was built up by successive layers of basalt
ship", one of the scenic features, while sedimentary
temporarily blocking the river. Eventually, however,
