Geology Reference
In-Depth Information
Jumpoff Joe along the coast near Newport showing erosion in 1900, 1913, and 1926. Only a small
knob of the original rock remains today (photo courtesy Oregon Dept. Geology and Mineral Indus-
tries).
marram grass growing on the surface.
The unusual number of lakes found on the
Clatsop Plains are elongate depressions between the
ridges of the dunes. The 1 to 2 mile long basins are
filled by groundwater percolating through the sand, and
most of the lakes, as Cullaby, Smith, and Coffenbury,
are independent of the local stream and river system
with no surface water running in or out.
climb to the top provides vistas of the Cascades, Mount
St. Helens, the Columbia River, and the city of Astoria
on the Pacific Ocean.
The 2,000 feet of dark basalts that make up
Saddle Mountain are part of the Miocene Columbia
River series extruded from fissures in northeastern
Oregon and southeastern Washington. Moving west-
ward down the ancestral Columbia River gorge, the
lavas eventually reached the Oregon coast. Where the
flowing lava encountered water, as is the case with the
basalts making up Saddle Mountain, breccias or broken
fragments of basalt and characteristic oval-shaped
pillow lavas resulted. Once the lavas had filled the local
stream valley and cooled, sedimentary rocks enclosing
the basalt were dissected by streams to expose the mass
of breccias at the crest of Saddle Mountain. Also
evident on the mountain are extensive vertical dikes of
basalt running through the breccia for hundreds of feet.
The dikes formed when the lava penetrated soft
Coastal Mountains
Dominating the skyline for miles in either
direction, Saddle Mountain, one of the highest peaks
in the Coast Range, projects 3,283 feet above the
surrounding countryside. Located in Clatsop County
just east of Seaside, Saddle Mountain was first noted
and named by John Wilkes of the U.S. Exploring
Expedition in 1841. Now part of Saddle Mountain
State Park, the towering cliffs and surrounding forests
make it one of Oregon's most remarkable spots. A
