Geology Reference
In-Depth Information
As viewed from the west, Humbug Mountain is composed of Cretaceous sandstones and conglomerates.
(photo courtesy Oregon State Highway Department).
Along the southern coast, Cape Ferrelo, Crook
Point, Cape Sebastian, Sisters Rocks, Humbug Moun-
The elongate Battle Rock, prominent at the
tain, and Nellies Point at The Heads project as the
cove south of Port Orford, was the site of a conflict
dominant headlands. Although most are composed of
between Europeans and Indians in 1851. A sea captain,
Jurassic Otter Point Formation rocks, the promontory
William Tichenor, sailing into the harbor, left behind
at Cape Sebastian is geologically unique because it is
9 men to begin a settlement. The men, attacked by the
one of the few coastal areas where late Cretaceous
resentful Indians, took refuge on Battle Rock which
rocks occur. Here massive 900 feet thick sandstones
projects above the water, until they could prudently
and siltstones of the Cape Sebastian and Hunters Cove
escape to the settlement where Reedsport is located
formations form the precipitous sea cliffs that extend
today. Composed of Mesozoic basalts, the rock is an
around Hunters Cove on the southeast side of the
obvious natural landmark in the area where a number
cape. North of Cape Sebastian, the small headlands at
of offshore stacks line the coast.
Otter Point and Sisters Rocks as well as Nellies Point
The most noticeable aspect of the southern
are braced by resistant Jurassic sandstones, mudstones,
Oregon coastline is the countless offshore stacks and
and volcanic rocks. The Heads mark the southern end
shoals, many of which are part of the Oregon Islands
of a Pleistocene terrace.
National Wildlife Refuge. The age, composition, and
The highest point on the southern coast, Hum-
arrangement of the rocks indicate they were originally
bug Mountain, a rounded promontory overlooking the
connected to the mainland at a time that it extended
ocean, offers a sweeping view of the shoreline and
further to the west. Once erosion shifts the shore
ocean to anyone willing to climb the 3 mile long trail.
landward, rock masses are cut off as isolated stacks,
A coarse bed of boulders at the base of the mountain
arches, and small knobs. Many are clustered in groups
grades upward into sandstones of the early Cretaceous
above the water level, while others are exposed only at
Humbug Mountain Conglomerate. On the south side
low tide.
of the mountain, huge cohesive blocks of rock, sliding
Along the southern-most section of the Oregon
into the ocean, deposit rubble and massive piles of
coast, Hastings Rock, rising 100 feet above the sands
debris along the shore faster than the sea can carry
just south of Brookings, was once a sea stack when
them away.
higher ocean waters covered the terrace. Nearby
