I'm not sure how Ft Lewis rates as a post as I've not been in the military. I have visited a few times and from a visitors POV it looked nice.
But the offroading sucks . . . .
Lame area at Rimrock.
Another sucky place to be bored in Manastash.
Pointless trails at Reiter.
Evan's Creek . . . . why bother.
Seriously, though. . .
Ft. Lewis is juuuuust south of Tacoma and nicely situated so you're not far from some great trails around the state. And by "not far" I'm talking 40-ish minutes to an hour. With some of the furthest trails maybe 3-4 hrs away.
This is what we have around Ft. Lewis:
Less than 1 hr Away
Tahuya ORV Park
Mostly for motorbikes they have been improving several routes for 4x4 Jeeps and other rigs. I've been here once a decade ago and wrote it off as lame but a lot of work by the state and REALLY dedicated locals has now transformed some trails into stuff that's probably more difficult than I can handle. So I'd put it back on the "go visit" list. Though I think total trail milage is still limited. Located in state forest land among 2nd or 3rd growth evergreen trees (there's tree cover but the trees are slim).
Evan's Creek
One of my favorite places to go wheel'n. The trails are interesting, though not super tough. A stock Jeep can run them with some winching, risk of rocker panel damage, and maybe rubbing the undercarriage skid plates. Modified Jeeps shouldn't have issue. Long wheelbase vehicles will find it VERY tight in several places. Located in the foothills surrounding Mt. Rainier JUST on the NW corner of Mt. Rainier National Park the ORV area starts at about 3700 ft of elevation and ranges up to 4800 ft of elevation. Snow covers the trail during the winter but there's usually good wheel'n from April through November before the snows come. Even in the snow its' fun but challenging. Trails range up and down the side of mountains and there are a number of tight switch backs. Trail bed consists of sloppy, slick mud and slimy roots and logs when wet. Run by Forest Service.
Elbe Hills ORV Park
Probably pushing the 1 hr distance a bit but . . . State run ORV park on the eastern edge of Elbe, WA. Tight tight trails and sloppy mud holes. Usually a bit out of my league. That plus the distance (for me) and I don't get down here much. Also, the ORV park runs on active forest land so it's not so nice looking lately with some clear cutting going on. But it has several trails.
1.5 - 2 hrs away
Reiter Trails
This isn't an official ORV park but people have been wheel'n here for decades and the state and local governments are working to convert it to an official ORV park. Trails range from super easy stuff to really difficult, meant-for-buggies type trails with not that much in between. There's also a significant rock garden there . . . think rock crawling but with slimy mud on the rocks and logs that roll out from under your tires. Gets interesting. Several non-official areas to park and camp where you won't be hassled by anyone. Given the up-to-now lack of law enforcement oversite it's a bit of a no-man's land. I've not personally had a problem but you see abandoned vehicles, informal bonfires, and random trash people dump illegally. Several clubs come together a couple times a year to clean it up. Trails range over a 2000 ft elevation gain starting at 500 ft and go up to 2500 ft. Not often there is snow but lots of wet sloppy trails through typical NW forests. Two of the best trails were recently shut down due to water crossing issues. They may be reopened some day . . . if there is funding for significant bridge building. Probably be a while.
Walker Valley ORV Park
At the other end of Puget Sound from Ft. Lewis. A bit of a drive for you. There's day use parking and toilet facilities but no camping. Just east of Mt. Vernon, WA. Fun area that was getting funner. . . until the state clear cut some trees and the "trail repairs" consisted of laying down so much rubble and rock that a major trail basically turned into a gravel road. Grrrr.. Still, there are other trails to explore throughout the ORV area and it'll keep you interested for a day once a season.
Naches Trail
Seasonally open from mid-July to mid-November this trail crosses the Cascade Mt. Range via 4x4 Jeep trail on an old wagon train route dating back to 1853 and re-opened by old WWII Jeeps in 1953. It was recently honored by BFGoodrich tires as one of five great American trails. It's not too tough now but the western end of the trail has several steep climbs that are fun. Several meadows are skirted once at the top on the western end of the trail and it crosses the Pacific Crest Trail (hiking trail stretching from Canada to Mexico). The Naches drops into the Little Naches Basin in eastern washing ton. From there, a short 5-ish mile drive down a paved Forest Service road leads you to access the Manastash Ridge area.
2.5 - 3+ hrs away
Manastash Ridge
Oh yeah. My favorite area. 115 sq miles of territory in the middle of Washington state on the eastern edge of the Cascade Mountains criss-crossed by 4x4, ATV, and motorbike trails. This area will keep you busy for days and days. LOTS of opportunity for camping, either at prepped campsites or out on the trails. Lots of stuff to see with great views from the ridge and mountain tops, steep hill climbs, Moab-like rock crawling, secluded lakes, surreal rock gardens, forest trails, incredible blue skies, and secluded lakes.
Rimrock
Another big area with LOTS of trails, trail milage, steep steep hill climbs and tons of camping and other recreation opportunities. My club typically spends 1-2 weeks here each year. Make sure your cooling system and brakes are in top notch condition as the trails are very steep. Awesome views from the ridge tops. A river runs down the main valley, there's a small alpine lake on top of a ridge, and the BIG Rimrock lake down below. Nearest gas station is a 90 min round trip away and you can burn up about 4+ gallons just getting from the gas station to the trail head. Bring some gas with you to refuel at camp. Oh, and best explored during a multi-day camping trip as it's a bit remote.
Liberty / Table Mountain
Trail networks in the hills surrounding the near-ghost down of Liberty just north of Cle Elum and Ellensburg on Hwy 97. There are at least a dozen trails in this area and they range from easy to tough depending on weather conditions. Any water on the trails and they get slicker n' snot. Camping opportunities abound either in "official" camp sites or out on the trail. A few good vantage points for these mountinous trails. Be respectful of some of the prospecting mines you encounter as a few are still active and the miners can get a bit touchy about their turf. I've been here several times but keep meaning to explore it more.
North Cle Elum area
Not many trails and the ones up here aren't difficult. But they do up up high in the mountains and get plenty far back into the hills. Great views from the highest points that top out at 6000 ft. Can be cold at night even in mid-July and snow tends to stick around a while. Lots of camping opportunities, river opportunities, and there's the big Lake Cle Elum further down.
Photos
If you want to see what these trails are like, click the "Pictures" link in my sig.
.