Building Sisters

If we could find a way to transport ourselves back into ancient times of the Sisters Country - say about 300 million years - we'd require a boat to get around; a vast, warm sea covered the land. And at least one peculiar species of dinosaur was living in the warm sea in those bygone days.

Around three hundred million years ago - in addition to being underwater - the site of Sisters was probably nearer to where Black Rock Desert in Nevada is today - and the land we're standing on is still traveling westward.

Think of it: we're living on a plate of so-called "solid rock," measuring from four to 45 miles in thickness. All the time sliding along in a westerly direction on top of a sea of red-hot stuff about 60 miles in thickness, and thought to be about 1,000 degrees Fahrenheit.

And to make life even more interesting, what we're standing on is on a collision-course with a plate of reconstituted sea bottom under the Pacific Ocean that's going in the opposite direction, diving ("subducting" if you will) under us. If that doesn't put some excitement in your life, nothing will!

It is impossible to find any evidence of dinosaurs or fossil sea-creatures around Sisters now; if there are any, they're buried under miles of basalt, andesite, rhyolite lava and ash. However, over near Mitchell -about 100 miles east of Sisters - paleontologists have discovered vertebrae of Ichthyosaurs, whale-sized relatives of dinosaurs.

At the summit of the grade between Mitchell and Prineville, in a road-cut, there's fossilized remains of the muddy bottom of saltwater bays that contain imprints of leaves, fish scales and invertebrates. Evidence of ancient sea life.

The forces driving the North American Continent westward, and the ocean floor sliding under us, caused unbelievable havoc to the land over the millions of years it's been on the move.

The present-day site of Sisters was caught between a maelstrom of crushing land masses that eventually heaved up the granite, snow-capped Willowa Mountains near Idaho, and Klamath Mountains on the California border, folding and twisting ancient metamorphic rocks like ribbon candy.

With powers of that magnitude opposing each other - an inexplicable force that cracked the Earth wide open - it's no wonder we've got beautiful snow-capped volcanic mountains to the west of Sisters, and such lovely little volcanoes like Hinkle Butte east of town on which to place a fire lookout.

About thirty million years ago a line of volcanoes were born near the site of present-day Sisters, but as the crust of the earth inched westward, the now-extinct volcanoes also traveled westward, becoming the eastern slopes of the Willamette Valley, where they are known as the Western Cascades. Ash from these ancient volcanoes fell on thick forests of hard-woods, and today paleobotanists dig their fossilized leaves out of the flanks of Gray Buttes, near Madras.

Smith Rock State Park, northeast of Sisters on Highway 97, is also a remnant ash deposit of those early catastrophic volcanic events.

For millions of years, the crust of the earth cracked repeatedly in a north/south direction shaping immense fault blocks east of the old Cascades. Remnants of those ancient fault blocks are still visible today, such as Green Ridge, north of Sisters.

As the ocean-bottom under us was pushed into the upper parts of the red-hot mantel, the crust of the earth cracked continually, resulting in hot lava roaring toward the surface, a process that is still going on. Maybe that's what's causing the land to rise near South Sister. Time will tell; Geological Time that is, not Man Time.

If there's lots of iron and very little silica in lava coming to the surface, such an event will sometimes build shield volcanoes, like Belknap Crater on the McKenzie Pass, the scene of one of our most recent basaltic volcanic eruptions. Events like these are similar to what is happening on the Hawaiian Islands almost continually.

When lavas contain less iron and more silica, the result will usually be andesite volcanoes - named after the Andes of South America. These are explosive events that are exciting to witness; it's best to be miles away when it is happening. A few years back, Mount St. Helens, in western Washington, gave us a small example of what they're like!

Next week, we'll explore a little more of the volcanoes of the Sisters country...