Just north of Kachess Lake, Cooper River Tr1311 traverses some rough Polallie Ridge terrain, from the Salmon La Sac campground to Cooper Lake.
Pete Lake Tr1323 continues 2.4mi, then into the Alpine Lakes Wilderness, past Pete Lake and around Island Mountain, to Delate Meadow.
The first 1.5mi of Cooper River Tr1311 ascends 1000' as it traverses Polallie Ridge, then the trail settles into a steady but rugged ride to the lake.
From Cooper Lake, Pete Lake Tr1323 follows the valley floor, so covers much easier terrain than Cooper River Tr1311.
The wilderness portion of Pete Lake Tr1323 is off limits to biking, but the non-wilderness section is open to biking.
To the south of Cooper Lake, a 9mi (2500') Kachess Ridge Tr1315 OAB to Thorp Mountain offers some moderate, rolling terrain.
Kachess Ridge Tr1315 could be combined with Cooper River Tr1311, using FR4600 and FR125 to connect these two trails, or just ride each OAB and avoid the road climb.
The southern Kachess Lake ride is covered on the Kachess Ridge Tr1315 page.
Red Mountain Tr1330? Closed to bikes and includes a 1.9mi, 3000' (30%) unrideable/life-threatening descent.
The area topo map includes some of the wilderness trails to the north, closed to biking but worth checking out if up for a big hiking excursion.
Epic hike? A 17mi CCW loop of Waptus River Tr1310, Waptus Pass Tr1329 and Polallie Ridge Tr1309 covers some steep and very scenic terrain.
Cooper River Trail 1311, Kachess Ridge Trail 1315, Pete Lake Trail 1323
Polallie Ridge Trail 1309, Red Mountain Trail 1330, Tired Creek Trail 1317, Waptus River Trail 1310, Waptus Bluffs Trail 1310.2, Waptus Pass Trail 1329
Owhi Campground, Red Mountain Campground, Salmon La Sac Campground
Ranking consistently applied to all of the listed trails.