Here is a link to a USGS Press release (5/8/01) on the Three Sister's area and recorded uplift

Here's the first paragraph - the rest of the story at the link below:
There has been a slight swelling, or uplift, of the ground surface over a broad area of central Oregon, centered five kilometers, or three miles, west of the South Sister volcano in Three Sisters region of the Oregon Cascade Range, according to scientists at the U.S. Geological Survey. The Three Sisters region is located 35 kilometers (22 miles) west of Bend, Ore., and 100 kilometers (60 miles) east of Eugene. The uplift, which scientists say occurred between 1996 and 2000, covers an area about 15 to 20 kilometers (9 to 12 miles) in diameter. The maximum amount of uplift at its center is about 10 centimeters (4 inches). It is too broad and low to be noticed from the ground, and several close aerial inspections of the area have revealed no unusual surface features.

Canie

• Three Sisters Show Ground Deformation