I rode the main Olallie trail to the camp (the flat pad above the second set of switchbacks shown on the annotated map) and then continued on as many others have done to the top of Mt WA.
Here are directions and a map for anyone who wants to give this a try. It was 22.3 miles and 5,225 feet from the parking lot by Rattlesnake lake. Camp is 7.2 miles into that and roughly 3,100 feet, so you are looking at another 2k+ feet and 4.5 miles to the summit of Mt WA. Doesnt sound like much, but considering the workout to get to camp, it really is a moderately challenging ride.
Leave the camp and continue climbing and once you pop out and around the small ridge you can see from camp, you will descend a bit and cross the Mt WA hiking trail. Stay on the blue trail on the map, dont get on Mt WA trail here. I circled the intersection on the map.
Ride about 2.2 miles futher, out and around 2 more ridges of Change Peak, first it is new single track and then some road to trails stuff. You will come to a split, left is down to Change Lake and right is up to Change Peak and on to Mt WA. There is a small sign on a tree in the middle of this split that indicates just that. I circled this on the map.
After you turn right, you end up on a moderate grade gravel road cut sharply into the side of Change Peak that suddenly pops above the trees. I show this in orange on the map. Enjoy the climb ;-) and the views. This road passes Change peak and then runs along a shoulder connecting Change Peak with Mt WA. Views, views, views. Past the main viewpoint toward Mt Si, you go about 1/2 mile more on this road and then come to an intersection, also cicled on the map, and take the sharp right. Pedal a bit up this road and you will be in a large opening, with a road to your right and left and a scramble trail heading up right in front of you. Take that, it's a couple hundred feet up, maybe 1/4 mile.
There is first a south facing viewpoint looking at Mt Rainier and the Seattle Watershed, then a bit more up the scramble you look out over North Bend and Mt Si. The views are insane.
It's a great ride, my own opinion is that the additional miles between the camp and the peak will require most to pack some extra food, I'd recommend "real food" like a sandwhich/etc. There is a nice view and even some shelter in the trees at the peak for when the colder weather rolls in. But it's just that much more of a ride than what we have around here, so unless you train on 20+ mile rides with 5k feet of climbing you will get sapped and not be able to enjoy the downhill ride back to the car without a good refueling stop at the top.