This is a much shorter list than the places where you can't. MTB missoula has a pretty good guide to the regulations, but no real specifics. You might read this:
https://www.mtbmissoula.org/post/e-bikes-what-you-need-to-know
And then wind up a little more confused than you were before. What is clear, is that as far as the USFS is concerned, they are a motorized vehicle. So on forest service land, you can only ride them on open roads and OHV (dirt bikes, atvs, etc) trails. A gate on a forest service road means it's closed to motorized vehicles, and yes, even e-bikes. Soo, if you're looking for somewhere to ride an ebike on FS land, the best way to see where you can go is to look at the motorized use maps. To find these, you can search for something like "lolo nf mvum" and a link like this will come up:
https://www.fs.usda.gov/detailfull/lolo/maps-pubs/?cid=stelprdb5097692&width=full
Those are all for the lolo national forest, which is where we are in missoula. Other nearby forests are the bitterroot and superior ranger districts, which have their own maps. Roads and trails on these maps open to motor vehicles and ebikes are highlighted.
Also you can look at a full mvum in arcgis here:
https://www.arcgis.com/home/webmap/viewer.html?useExisting=1&layers=18de7e3f022a432f850c864ad4ba952d
In case it wasn't clear, all the trails in the rattlesnake are closed to ebikes. As are the marshall mountain trails, mount sentinel, and pattee canyon areas. You can't even ride one on the deer creek sneak. But you can ride up deer creek road, and up above pattee, to the miller divide trail. Also in that area are a number of roads like allen creek from turah and holloman saddle, and it's mostly all open to e-bikes.
The other part of missoula that allows e-bikes is Blue Mountain. But not very much of it- just the parts open to motorized vehicles such as deadman's ridge, orchard, and hayes creek. One thing to note about this is that motorized use on those trails is seasonal. In the spring when the gate on the road is closed and you can't drive to the moto trailhead, all those trails are also closed to motorized use, and yes, e-bikes. But if I had an e-mtb, blue mountain, and all the area beyond, is where I'd spend most of my time. From the top, there are a lot of places you can go, like all the way out to the southside road, petty creek, or highway 12.
Speaking of highway 12, I noticed one trail on the mvum that I didn't expect to see - mill creek on lolo peak. However, to ride it you have to do an out and back from the bottom- the section from the mormon peak road trailhead does not allow e-bikes (and neither does the trail from carlton ridge).
Going farther up highway 12, there are also some lines on the map in the graves cr/petty cr and lolo pass areas. Whether the trails exist and are clear is another question, but they're there.
Eventually I'll probably make a public map on caltopo with some of these routes and trails and roads highlighted but for now I'm about done typing. Here's a list of some of the trails that are open to ebikes
Miller divide 512
Mill Creek 1310
Ninemile divide
blue mountain
telephone butte area
1220
720
lolo pass/lolo hot spring/petty creek/wagon mountain area
26
322
289
295
skookum butte
Bitterroot-rock cr divide 313
sweathouse creek
121
122
Warm springs, lost trail pass area is almost all open to motorized use
