The name of this state park is a little misleading - there is no waterfall in the park named Silver Falls! Instead, the north and south forks of Silver Creek cascade into a canyon network surrounded by dense temperate rain forest. The Trail of 10 Falls is a spectacular hike that passes by (and behind, in more than one instance) waterfalls ranging in height from 27ft to 178ft. A note to the adventurer - the seven mile trail will be wet and slippery in places on the best of days. On a rainy day it can be a challenge.
South Falls is the most accessible and most frequently mislabeled"Silver Falls." The spectacular freefall drop of 177 feet into a large pool and the large amphitheater and trail behind the fall make it a particular favorite. It's an easy hike on paved trails down to the creek and around behind the falls. The walk is highly recommended.
Part of the adventure of Silver Falls can be the trip getting there. Traveling from Portland, take the Stafford Rd. exit off I-205 south to Mountain Rd., crossing the Willamette river on the Canby Ferry ($2 toll) and traveling through the beautiful farmland of the Willamette Valley. Here's a map. It makes a nice weekend afternoon outing from Portland, stretching into the evening with dinner in Silverton.