It’s hard to believe that 18,000 years ago a gigantic ice cap covered the Cascade Range, up to 2,000’ thick and 170 miles long. Glaciers filled nearly every canyon with moving ice, sculpting the landscape. Much evidence of this glaciation is lost to erosion and volcanic activity, but is still well-preserved today in the headwaters of the Little Deschutes River. Here one finds a classic U-shaped canyon, 1,500’ deep with moraines and a meandering stream, easily explored on a 2-mile trail (one way) and cross-country forays.

Of all the buttes in Central Oregon, only a few are hydrovolcanoes, where rising magma intermixed explosively with surface water (such as a lake or underground aquifer) to form a layered ring of solidified volcanic rock known as tuff. One of the more accessible but less-visited of these picturesque tuff rings is Moffitt Butte, just a 50-minute drive south from Bend, off of Hwy 31. Here a 2.6-mile (roundtrip) closed road hike leads up into the tuff ring with long sweeping views, plus cross-county treks to dramatic tuff formations around the rim.

Located on the northern edge of the Fort Rock Basin 60 miles south of Bend, the Devils Garden Lava Field is a 45 square mile maze of lava tubes, spatter cones, tumuli and kipukas. These broad flows of pahoehoe lava are not barren like many in Central Oregon, but feature ponderosa, juniper and mountain mahogany. This flora supports a rich variety of wildlife, including mule deer, bighorn sheep and fabled “lava bears.” Best of all, it's easily explored on a 2.1-mile jeep road hike through the lava field to pine-covered Little Garden kipuka.

It was one of Oregon’s highest peaks, over 12,000’ in elevation. It was taller than Mt. Hood and more massive than Mt. Jefferson. But in a matter of hours 7,700 years ago, it disappeared in one cataclysmic explosion, sending ash deposits as far away as Canada and hot pumice flows hundreds of feet thick up to 25 miles from today’s Crater Lake. The distinctive, white-colored signature layer of these tephra deposits can be found throughout Central Oregon today, revealing itself at trailside or on riverbanks when least expected.

Hidden and nearly unnoticed in the canyon lands above the Metolius River arm of Lake Billy Chinook are several small bowls with unique geologic formations, known as the “balanced rocks.” Carved by erosion over eons of time, these great slabs of rock weighing many tons are poised up to thirty feet in the air above pinnacles of softer rock. First recorded in 1855 by a railroad survey party traveling in the area, these balanced rock formations are accessible today by a short hike from a good road about thirty driving miles west of Culver.

In our scientific age, it’s hard to believe that the origins of any landform could still be unexplained, but this is the case with the extensive soil mounds and their encircling rock rings found northeast of Madras on the Shaniko Plateau. Known as mima (my-muh) mounds, several theories have been advanced about their formation, from differential erosion, to Ice Age freeze-thaw cycles, to soil movement by foraging gophers. But no one theory is widely accepted and these unusual land features remain a puzzle to geologists today. Hundreds of acres of this mima mound topography can be explored on BLM land near Shaniko.

What are tumuli (besides the plural of tumulus)? From the Latin tumidus, meaning swollen or bulging in shape, a tumulus is a circular, domed lava structure up to 30’ high and 60’ in diameter, formed by the upward pressure of actively-flowing lava against its cooling crust. Along with its elongated cousin, the pressure ridge, these fascinating lava formations can be explored on a less-traveled trail in the Badlands Wilderness, just 15 miles east of Bend.

Some of the more geologically and visually interesting canyons in Central Oregon are found on the southeast slopes of the Crater Lake caldera. In these lightly-visited canyons are found hundreds of stark stone pinnacles, which have eroded out of the volcanic ash of remnant Mount Mazama. The pinnacles in Wheeler Canyon are easily accessible by car at a viewpoint in Crater Lake National Park, while the rock towers in lower Sand Canyon require a challenging, cross-country bushwhack of 2.7 miles roundtrip.

One of the more interesting geologic features of Central Oregon are kipukas (meaning “a variation or change in form” in the Hawaiian language). These are islands where lava has surrounded patches of older terrain, isolating them from the surrounding landscape. It’s hard to imagine a more dramatic contrast between the dry, rocky, barren fields of lava surrounding the relatively moist, shady islands of forest.