Who's fault is it?

About 40 million years ago, a swarm of andesite volcanoes along the Brothers fault line east of Sisters left behind hundreds of square miles of mud-flows that trapped leaves and seeds from the trees that lived near here at the time. Fossilized miniature coconuts and palm seeds have been found in the rock-like ash near Fossil.

Some geologists believe that southwestern Oregon is being hauled along toward Alaska with part of California - hooked to the San Andreas fault system. A line along the Brothers fault may mark the eventual separation of western Oregon from eastern Oregon.

Sisters' faults are nothing compared to Brothers' faults. Many of the recent volcanic events (from a thousand to 1 million years in age) are in the vicinity of the Brothers fault, which begins near Sisters and terminates near the Oregon/Idaho border. Newberry Volcanic Monument is one of them.

Our front-yard volcano - 6,400-foot Black Butte - rests on what may be where the Brothers fault system ends, slammed up against Green Ridge. Fryrear Butte, near Tumalo, is thought to be about the same age as Hinkle Butte, perhaps a million years old.

Basalt lavas flowing from the Cascades, left behind layer after layer of pahoehoe and ah ah lavas, riddled with lava tubes. The Sisters countryside has several of these lava "caves" to explore. Sawyer's Cave, alongside the South Santiam Highway, and about 2.5 miles west of Santiam Junction, is open for year-round exploration.

Skylight Cave is located about 12 miles northwest of Sisters, almost midway between Sixmile and Fivemile Buttes: Skylight Cave can be explored in summer.

The snow-capped Cascades we gaze upon to the west are the results of the continual lifting and cracking that opens the earth. As the surface slowly rises, something has to give, and when it does the earth cracks in a north and south line, allowing lava lakes beneath us to release their forces.

The result is a line of volcanoes stretching from Mt. Garibaldi in Canada to Mt. Lassen in California - known today as the Cascade Range.

As the Cascades exploded their gases and built towering snow-capped composite volcanoes, other events piled more and more lavas and rock debris on the countryside. Three Creeks, Melvin Butte, and the Tumalo Highlands, visible from Sisters, are silent reminders of the violent forces under our feet.

As the Oregon countryside was lifted up, lava flow after lava flow added to the land. About 30 million years ago the earth cracked open in a north/south line near where Walla Walla, Washington, is today and issued forth basaltic lavas that are in some places 10 miles thick, virtually burying all record of ancient Oregon's past.

Those lavas are still visible today, towering above the waters of Lake Billy Chinook, north of Sisters, and remnants can also be seen all the way to the Oregon Coast, where a few stand as sea-stacks, resolutely resisting the forces of the Pacific Ocean.

Far to the south, Mt. Mazama grumbled into life about 7,000 years ago and exploded with such power that it showered ash from near Ashland all the way to Canada, leaving behind Crater Lake National Monument, the "Jewel of Oregon."

That enormous pumice eruption changed the soils so dramatically that sprawling forest of tamarack vanished almost completely, and pines and firs sprang up instead. Only small remnants of the tamarack forest can be seen today around the Cascade foothills in the Sisters Country.

The battle between fire and ice was never a peaceful one, nor one-sided. While the glaciers were grinding away at the Cascades, South Sister retaliated by exploding immense quantities of ash and lavas into the ice and snow.

When the vast ice shields and glaciers began to melt and free the Cascades from their icy jackets, the resulting floods carried chucks of lava, ash and gigantic boulders down into the countryside all around Sisters.

One of the reasons this country is so rich for farming is because of the soils accumulated during the floods of the last Ice Age. All the flat areas around Sisters are the results of huge lakes formed as ice slammed into tight spots in the Deschutes River, creating short-lived ice dams that backed up ice melt all the way to the foothills of the Cascades.

During the melting process water was in a big hurry to get back to the sea, which was about 400 feet lower than it is today.

The resulting deep canyons of McKenzie and Dry Canyons - between Sisters and Redmond - are mute evidence of how the melt-water created some of the most breathtaking landscapes in Oregon.

Will a few of the snow-capped volcanoes erupt some time again? Most geologists believe they will. It's only a question of when.