Geology Reference
In-Depth Information
gas. In the Willamette Valley a number of drill sites
showed oil and gas, and in 1981 a well near Lebanon
in Linn County tested 170,000 cubic feet of gas per day
before it was plugged and abandoned. Oil and gas have
also been reported in the Tyee basin of the southern
Coast Range.
Drilling of the Mist region in Columbia
County began in 1945, but it wasn't until 1979 that the
gas field here was discovered by the combined efforts
of Reichold Energy Corporation, Diamond Shamrock
Corporation, and Northwest Natural Gas Company.
Today the field consists of 18 wells, producing 38.4
billion cubic feet of gas to date, with no significant oil.
Most of the reservoirs in the field are fault traps within
a larger anticline structure. Hydrocarbons found in
sandstone reservoirs of the upper Eocene Cowlitz
Formation initially accumulated in organic-rich marine
deltaic sediments before being transformed by heat into
gas.
The Beaver Hill Coal Mines in the Coaledo Forma-
tion reflect an industry from Oregon's past (photo
courtesy of Oregon Dept. Geology and Mineral
Industries)
Throughout the Pacific Northwest, several
fine-grained sedimentary rocks are regarded as poten-
tial sources for petroleum. However the lack of porous
reservoir rocks is largely due to clays and zeolite
minerals plugging the sandstones. The most likely
reservoir sands are those deposited in high energy
upper continental shelf environments where volcanic
debris is limited. The Cowlitz, Yamhill, Coaledo,
Spencer, Eugene, Yaquina, and Astoria formations
meet these conditions in part. Similar requirements for
reservoir rocks need to exist for the successful explora-
tion for offshore oil. Even with the limited success of
Oregon petroleum exploration, it would be premature
to say all available resources in the state have been
expended.
car more than 3 to 4 feet deep will often begin to
smolder and burn.
The Coos Bay coal field in the Beaver Hill bed
of the Coaledo Formation, 30 miles long and 12 miles
wide, is situated with the long axis in a north-south
direction. After its discovery in 1854, the Coos field
was mined sporatically through the 1940s at which time
modern machinery was installed. Between the middle
1800s and 1920, the recorded production from 37
mines was 3 million tons. The potentially dangerous
shafts and portals of the mines were sealed and covered
in 1985 as a safety measure completed by the U.S.
Office of Surface Mining, temporarily ending the
Oregon coal mining era.
Coal in the Eden Ridge field in southern Coos
County is part of the Tyee basin sediments. Here
significant amounts of sub-bituminous coal were
located by extensive drilling during the 1950s, but
commercial exploitation has never been feasible.
Mercury
In western Oregon cinnabar or mercury ore
occurs scattered within a belt 20 miles wide that
extends from Lane, Douglas, and Jackson counties in
the southern Coast Range to the California border. In
Lane County, the Black Butte and Bonanza mines are
responsible for about one-half of Oregon's quicksilver
production. Mining here exploits Eocene marine
sediments as well as volcanics of the Fisher Formation.
Discovered in 1890 by S.P. Garoutte, the Black Butte
Mine yielded a reddish cinnabar ore. Sulfur, combined
with the mercury in the ore, was burned off in a 40-
ton-a-day furnace. The mine was operated off and on
until the early 1970s when the land containing the
mine was sold for its timber assets.
Slightly to the south in Douglas County, cinna-
bar at Bonanza Quicksilver Mine was found in the
1860s. The mine was operated under a succession of
owners during World War II when wartime demands
Oil and Gas
Exploration for oil and gas in the Pacific
Northwest began about 1881 with reports of "smell
muds", oil, and gas seeps along the Washington coast.
Almost all of the 500 exploratory wells were drilled
prior to World War II, but only about 80 penetrated
below 5,000 feet. Drilling activity in Oregon has been
sporatic since the early 1900s. Wells drilled near Coos
Bay after 1930 record minor amounts of both oil and
