Rock Formations
- The Clarno formation, rock strata stemming from prehistoric volcanic eruptions, anchors a broad belt from central to northeastern Oregon. Active during Eocene time some 50 to 40 million years ago, the Clarno volcanoes are kin to the modern Cascade Range: Like Mount Hood and the other famous peaks of that chain, they erupted from the molten rock produced as Pacific tectonic plates plunged beneath the leading edge of the North American continent. Southward from Clarno into the Ochoco Mountains, you can see telltale cones and knobs representing the eroded-down innards of these old volcanic peaks. Meanwhile, layers of hardened ash, andesite lava flows and volcanic mudflows, or lahars, cover large portions of the region. When the Clarno volcanoes were erupting, this part of Oregon enjoyed a warm, moist climate, and the violent debris flows preserved remains of palms, cycads, magnolias and other subtropical plants, along with crocodiles, brontotheres, pint-sized horses and other exotic beasts. Later, the Clarno layers were partly covered by volcanic ash ejected by the Western Cascades and by floods of basaltic lava emitted from vents around present-day Monument.
Buttes and Hills
- The intermixed layers of tuff, lava flows, lahars, sedimentary formations and flood basalts, lurched about by faulting and sliced into by creeks and rivers, make a rugged landscape in the Clarno area. You’ll see soft, rounded hills, gently sculpted out of pliable tuff and sedimentary rock, contrasting with flat-topped buttes capped by hard basalt. Touring between the three discrete units of the John Day Fossil Beds National Monument – Clarno, Sheep Rock and Painted Hills – acquaints you with such scenery.
The Palisades
- The defining landmark of the Clarno Unit of the John Day Fossil Beds National Monument is a high rim of pinnacle cliffs called the Palisades. Like architectural ruins rising above a sloping grassland pediment, these leave the motorist on Route 218 approaching the site wonder-struck. Some 44 million years old, the Palisades are the petrified remnants of Clarno volcanic debris flows. A system of short paths from the Palisades trailhead offers outstanding opportunities to immerse yourself in the geological story: On the Trail of the Fossils, you’ll pass boulders cleft off the Palisades and tattooed with plant fossils, while the Clarno Arch Trail reveals a natural rock arch. The story is made all the more explicit by the Geologic Time Trail linking the trailhead and a picnic area a quarter-mile east, on which hikers noting the informational signs take a symbolic trek through the ancient past.
Exploring
- Aside from the excellent trails in the Clarno Unit, make sure to fully explore the Sheep Rock Unit -- named for a banded cone displaying 40 million years of geologic time -- and the Painted Hills, sensual, otherworldly badlands streaked with rusted Clarno clays. Don't miss the monument’s large visitor center at Sheep Rock, which displays plenty of plant and animal fossils amid immersive dioramas. Closer at hand is the Spring Basin Wilderness just southeast of Clarno. Managed by the Bureau of Land Management, this wild place -- excellent for cross-country hiking -- drops from peaks like 2,827-foot Horse Mountain to rough gulches like Hay Bottom and Eagle canyons, where Clarno formations are exposed. Boaters savor 70 miles of the rugged, basalt-ribbed John Day River canyon from Clarno downstream to the Cottonwood Bridge.
Ecological Frontiers
- From a topographic map, you can easily appreciate Clarno’s position at the northern edge of the Blue Mountains, which arc southwest to northeast across central and eastern Oregon. North of Clarno, the John Day River enters a deepening canyon striking across the Deschutes-Umatilla Plateau, a rolling upland built upon the deep flows of Columbia River Basalt. From the vicinity of Clarno, you can look northeastward to the scarp marking the commencement of this plateau, part of the larger Columbia Basin province; look for the dark, younger basalt layers atop the lighter-colored strata of the John Day country.
