Like
Sacajawea,
Matterhorn
is composed
mostly of
marble.
FALL HIKING
Continued from Page 23
As you climb away from Falls Creek a
view to the southeast opens and Sacajawea,
the Wallowas’ highest peak at 9,838 feet, ap-
pears. It’s a gray-colored mountain, composed
almost entirely of marble. To geologists, mar-
ble is nothing more than limestone that has
been metamorphosed — recrystallized by
heat and some pressure. The light-colored,
gray rocks that comprise Sacajawea, Matter-
horn and the lower portion of Hurricane Di-
vide to the west are all limestones that were
metamorphosed by the intrusion of the “gran-
ites” that form the core of the Wallowa Moun-
tains. These limestones (now marbles) are
about 200-230 million years old. In places
where they are less altered they contain fos-
sils, including corals and “clams.” But fos-
sils in the rocks of Sacajawea, Matterhorn
and Hurricane Divide have been obliterated
by heat and pressure.
In addition to being the highest peak in
the Wallowas, Sacajawea also rises 1.2 verti-
cal miles (6,377 feet) from its base on Hurri-
cane Creek. The climber’s website Peakbag-
ger.com says it is the second most prominent
peak in Oregon. Only Mount Hood rises
higher above its surrounding terrain.
24 | Experience the Wallowas
As the landscape opens to views of Hurri-
cane Divide west of the trail, you’ll see dark
layered rocks atop the gray marbles. These
are sedimentary rocks — mostly sandstones
that, like the marbles beneath them, have been
heated and metamorphosed. The marbles and
banded or layered “sandstones” appear along
the trail, especially at stream crossings.
You’ll also notice narrow streaks of dark
red-brown rocks that slice through the gray
marble. These are basalt. Speciically, they
are the issures or “dikes” that allowed dark,
luid, iron-rich basalt lavas to reach the sur-
face (far above today’s peaks) and erupt. The
eruptions — about 14-16 million years ago
— produced the Columbia River basalts, the
lavas that covered the Columbia Basin, and
lowed all the way to the Paciic Ocean.
You can get up-close and personal with
one of these dikes at Slick Rock Creek.
About 3 miles into the hike, the trail switch-
backs and then creeps along above a steep,
narrow gorge sliced into marble before lead-
ing to Slick Rock Creek. Here, a waterfall
cascades over a dark cliff. The dark cliff
at Slick Rock Creek is part of a Columbia
River basalt dike.
Beyond Slick Rock Creek you’ll ind
patches of open meadows that open views
of granite peaks to the south, and inally, the
marble face of Matterhorn. The dark lines that
mottle its north face are more Columbia River
basalt dikes. The vegetation begins to change.
Subalpine ir increases, Douglas ir decreas-
es and Ponderosa pine vanishes. Large Engel-
mann spruce are the patriarchs of the valley
loor.
“Granite” outcrops don’t appear along the
trail until about 8 miles into the 10-mile trek,
at the threshold of the Lakes Basin. These
black-and-white, speckled rocks are about
120 million years old — much younger than
the greenstones, marbles and “sandstones”
but much older than the basalts. Granites,
strewn with dark red-brown basalt dikes form
the core of the Wallowas, and occupy the en-
tirety of the Lakes Basin.
If you venture into the Wallowas in the
fall, be sure you are prepared for cool to cold,
wintry mountain weather. This means base
layers and mid-layers of clothing that will
keep you warm. Also, waterproof, insulated
boots, hat, warm gloves, warm and water-
proof jacket(s), ire-starter and stove, water,
lashlight and/or headlamp, shelter and extra
food at a minimum are in order.
Be sure to let someone know where you
are going, and when you will return.