Each volcano on this list is on the US Geological Service’s list of ten most likely to erupt volcanos. Working from North to roughly south, each of these is less then a days drive from Portland.
First up is Mt. Rainier, presiding over Seattle and Tacoma.
Next is Mt. St. Helens, famous as it’s recently erupted. (As far as Volcanos go anyways.)
Mt. Adams which is up the Columbia Gorge a ways and viewable from Hood River.
And then Mt. Hood. Viewable from Portland, Vancouver, Gresham, Sandy, Hood River.
The Three Sisters, near Bend and Sunriver. I think the northern one is the most volcanic, but not sure. There is also the nearby Newberry Caldera just south of Bend which is highly volcanic.
And just in case you needed some evidence of the volcanic activity here, check out this Seismograph Map of recent earthquakes.
Fort Rock is one Oregon’s geologic treasures. Created between 50,000 to 100,000 years ago from lava venting into the muddy bottom of what is now called Fort Rock Lake. The resulting steam explosion threw ash and basalt particles up into the air which rained down in a circular formation around the vent. The explosion also caused huge basalt blocks to thrust upwards. This is actually fairly common in central Oregon as about 40 of these formations exist as far north as John Day, Oregon.
The actual Fort Rock
The days of explosive lava are long over, but the area has significant historical importance. In 1936 Dr. Luther Cressman from the University of Oregon found sage brush sandals that dated back 9300 years. At the time this turned the Archeology world on it’s head as up until then humans were only thought to have been on the North American continent 5000 years ago.
Across the street is the Fort Rock Valley Historical Homestead Museum. The museum was created to save several old homestead buildings from being destroyed to make way for cattle farms. Each building was taken apart, moved to the museum and restored. Most of the buildings now have mini-museums in them showing artifacts from daily life in the era. In addition to several log cabins, there is a church, a Doctor’s Office and a one room school house.
One Room School House in Fort Rock, Oregon
Unfortunately the museum itself has been closed every time I’ve been by it. This area is within a day’s drive of Portland and several nearby camp grounds provide over night opportunities. The museum and Fort Rock itself along with the famous Sandal Cave would easy take a day to explore. Nearby geological formations like South Ice Cave and Crack in the Ground would be great for a home school history/geology trip.