We are going to be up in southwestern Montana and northern Idaho in August. Does anyone have some 'must ride' trails to recommend? We love getting into the highcountry with our average rided being 12-18 miles. We will be camping at our trailer.

Any suggestions welcome :)

Sarah

http://www.fourcornerstrails.com/

In SW Montana, there are hundreds of miles of horse trails arising out out of the Bitterroot Valley alone, and you can't go wrong with most of them.  A couple of very good starting resources for you would be:

1) the quite comprehensive listing of trails and facilities by the Bitter Root Back Country Horsemen at http://www.bchmt.org/bitterroot/BBCHforms/Trails4HorseStock.pdf 

2) the Bitterroot National Forest Service updates on current trail status and conditions listed at http://www.fs.fed.us/r1/bitterroot/recreation/trails/trail.shtml

A couple of personal favorites for me in this area, which would seem to meet your criteria are:

Easthouse National Recreation Trail (#313)
Starting at Sawmill Saddle (elev. 6,600 ft.) on the Bitterroot/Rock Creek Divide southeast of Stevensville, MT, trail #313 traverses south into the 103,000 acre Stony Mountain Roadless Area and threads along the crest of the Sapphire Mountains for approximately 70 miles until it joins the Continental Divide National Scenic Trail in the Anaconda-Pintlar Wilderness. 

The northern 23 miles of trail #313 from Sawmill Saddle to Skalkaho Pass has been designated as the Easthouse National Recreation Trail.  Fourteen connecting trails provide multiple opportunities for access and loop trips. One fork of the trail connects with the Palisade Mountain Trail mentioned below.

Much of trail #313 is above timberline, between 7,000 and 8,000 feet. Snowpack may be an issue.  Be certain to check the current trail conditions listed on the BNFS web site above, or give the FS a call before departing.  The trail provides multiple spectacular vistas of both the Pintlar and Bitterroot mountain ranges, with plenty of opportunities to observe wildlife.

ENR Trail Begins:  Sawmill Saddle on Forest Road 710
ENR Trail Ends:  Skalkaho Pass on Montana Highway 38 
 
Area Map: Bitterroot National Forest Visitors Map
USGS Map: Sawmill Saddle
USGS Map: Burnt Fork Lake
USGS Map: Skalkaho Pass

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Palisade Mountain Trail (#44)
The 6-mile long Palisade Mountain Trail skirts the northern edge of the 20,000 acre Skalkaho Game Preserve and ends at Burnt Fork Lake in the Sapphire Mountains. Travel along the ridge trail offers views of the scenic Bitterroot Mountains and opportunities to see big game. The trailhead has a developed campsite, horsefeed-bunks, and hitch rails. Maintained every two years. Trail classified as moderate.

Length: 6.0 miles
Trail Begins: Forest Road 1348
Trail Ends: Trail 86

Area Map: Bitterroot National Forest Visitors Map
USGS Map1: Burnt Fork Lake
USGS Map2: Willow Mountain

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If you get a bit farther north in Montana, you should not miss the opportunity to traverse some of the thousands of miles of trails in or near the Bob Marshall Wilderness.  I can provide you with some details of a number of trails in this region if it's a possibility.

Wherever you go, with a little planning, you should have a terrific time!

A little farther to the South around Tetonia and Driggs you can ride into the west side of the Tetons.  Granite Basin is one of my favorites.  The trail head starts at North Leigh Creek and makes a loop up through Granite and down through the Green Lakes.

There are numerous rides in and around Yellowstone National park.  I really enjoy the trails out of the Bechler Meadow rangers station in the South West Corner of the Park. Nice easy trails that you can trot or gait along at a good clip.  And thre are a few hot springs to take a swim in along the way.

Union Falls in Yellowstone

Thanks guys! I am planning to do some riding around/in the Tetons and have been keeping an eye on Paintedhorse's post on my trail forum and this one (thanks Jon!). Thanks for the great suggestions and links!!!!

We live near Durango and have done a lot of riding in the high country here, and are really looking forward to seeing some different places and trails we've never been on.

We will be taking the horses to Seattle (will board them for a few days) to visit my sister and then take her camping and riding somewhere up there. Then we will take our time getting home :)