Update: A major wildfire has caused the area to be closed for safety reasons. No date yet established on when the area will be reopened but estimates are that it will be late spring, 2018
Tanner Butte appears to be one of the more rarely visited major Columbia Gorge peaks probably both for the long trail distances to get to it and the fact that the actual summit pitch has only a barely visible trail. Also, it probably doesn't help that the last several miles of trail is un-maintained. Nevertheless, this peak is most photogenic once you do get to it and the views from the summit are excellent including all five of the major cascade volcanoes from Jefferson to Rainier. The views of Mt. Hood from Tanner Butte are exceptional as the picture below attests:
Mt. Hood view from Tanner Butte Summit area.
There is evidence that a fire lookout once stood on the summit but there's nothing left now but a few bits of glass and metal. cmc56789 provided the following link for a pic and some data on the lookout: Link
The veritable maze of trails in the gorge provides many options for access but only a couple that are arguably do-able in a day of trail running or serious hiking. The following are my choices:
From I-84 take the Bonneville Dam exit 40 and turn south on the short road to the parking area. The unmarked trailhead is immediately to the left of the Wahclella Falls sign as you start down the parking area road. Alternately, turn left at the Wahclella Falls sign and drive up the short road to another parking area. This alternate access starts out up the gated gravel road (Road 777) to the right of the water storage tower and is about .48 miles shorter than the other trail. The added advantage is that it's easier to follow than the somewhat confusing trail. Whichever way you chose, the two routes soon meet on a closed-to-vehicle-travel gravel road in a little more than a mile. After another mile up the road, at a stream crossing, find the Tanner Butte Trail sign and go up the hill to the left. Follow this for another 6.9 miles and then find the sign for the unmaintained scramble trail to the summit. This faint trail winds another .48 miles up through the trees to the top of the peak. Total round trip elevation gain is 5,200' and 19.6 miles.
Another option is to take exit 41, (eastbound only) park at the Eagle Creek Trailhead and take the Eagle Creek Trail. I prefer this trailhead feeling it to be safer to leave one's vehicle parked in an area with a "Camp Host" on duty This is a bit longer at about 23 1/2 miles total and about 5,500 total vertical feet but has the advantage of the excellent sights along Eagle Creek. About 7.3 miles from the trailhead (the trailhead that starts at the turnaround at the end of the access road), on a left hand switchback, take the Eagle-Tanner Trail more-or-less straight ahead. The junction to this seldom-if-ever maintained trail could be easy to miss so if you find yourself going uphill in a northeasterly direction, you missed it. About a mile farther you will have to ford the un-bridged Eagle Creek: The best spot is upstream about 200 feet from where the trail stops at water's edge. Bushwhack straight up the opposite bank and rejoin the trail which parallels the creek a few dozen feet from the top of the bank. In another 3 1/2 miles, turn right at the Tanner Butte Trail junction, go about 1.2 miles and find the sign marking the scramble trail up to the summit. To complete the loop, go north on the Tanner Butte Trail turning right on Trail 400 to return to your starting point at Eagle Creek.
A Trail Park pass or equivalent is required at both exit 40 trailheads as well as Eagle Creek trailheads off exit 41. There is a self-serve pass kiosk at both the trailheads.
The usual national forest and/or wilderness rules apply.
When To Climb
Late spring through early November is best but hardy souls could do this as a snow shoe trip in the winter. The upper elevations will be very snow covered from Nov. through at least April. As of the end of June, 2008, 6 feet and more of heavy packed snow covers the upper reaches (above about 3,300') of both routes and runoff is heavy at the Eagle Creek ford so plan accordingly.
Primitive camping spots abound. A few even have a weathered picnic table!
Here's a link for the northern Oregon Cascades weather: Weather