From Portland, take HWY84 East. At the Ainsworth park exit (#35), take this exit and follow the Historic Columbia River Highway East up river for about 1.5 miles to the signed Horsetail falls parking area.
Loop hike up and around Oneonta Gorge in Oregon.
The Columbia River East of Portland contains a number of excellent hiking opportunities. One fun and easy trail is the loop hike and slot canyon exploration around the Oneonta gorge.
From the Horsetail parking area (be sure to enjoy the view of Horsetail falls), cross the road and start climbing up the well signed and easy to follow trail. It doesn't take long before you reach your first scenic reward, Ponytail falls. The trail actually cuts behind the waterfall, giving a very unique perspective. The trail continues to climb, roughly paralleling the highway and offering increasingly impressive views of the Columbia river area. As you reach the Oneonta gorge, the trail turns South and continues climbing. You'll reach a bridge crossing the gorge. Just on the other side of the bridge is a trail junction. Turn left here to walk up to Triple falls. From the bridge it's about 0.9 miles to Triple falls. Oneonta creek splits three ways as it drops down the gorge, creating Triple falls. The bridge crossing the creek at the top of this falls is a good turn around point for this hike. Head back to the trail junction, staying left this time as the trail drops back down to the highway (and an alternate parking area if Horsetail falls is too crowded). Start walking East (right) along the highway towards your vehicle. But the fun isn't over yet! About halfway to your car you'll cross the road bridge over Oneonta creek, just before the historic tunnel. There is a set of stairs on the right that allows you to drop into the gorge itself.
You will get your feet wet (and most of your body!) so dress appropriately and wear appropriate footwear. The water is cold year round in this creek. The narrow walls of this gorge increase the excitement of wading and scrambling towards the hidden waterfall (about 0.5 miles from the road). The first obstacle is a massive log jam. It will take a bit of time, since the logs are quite slippery. You'll need to make use of your scrambling skills here. After surmounting the log jam, continue upstream, walking in the shallow creek water. There is at least a chest deep wade (or alternatively some bouldering moves on canyon right to stay more dry) before you reach the waterfall. Not long after the wade you get your first view of the normally hidden Oneonta waterfall as it drops into the gorge. It's an impressive site and an excellent reward for your efforts. Backtrack to the highway and continue the final few hundred yards to your car.
Keep in mind that annual rains can easily change the hike up Oneonta gorge. The log jam may be gone or it may be worse! Be prepared and use good judgement.
Horsetail falls is a popular area, so parking could be problematic. If parking is full at Horsetail falls, backtrack to the alternate parking area shown on the map. Parking on the side of the highway is also allowed in areas, but be aware of no parking signs.