In the winter, drive on Salmon La Sac road until it ends at the trailhead. Turn around in the "no parking" zone and drive back the way you came until you reach a sign that says begin parking on this side of the road. We parked around 9 am and there was only one other truck in front of us. At that time the road was dry and snow free. Don't forget to display your sno-park pass. 

We started hiking on the groomed snowmobile and xc ski trail. A few snowmobiles went by leaving us in a cloud of 2-stroke exhaust. The trail splits pretty quickly and sleds go right and skiers and hikers go left. Continue along the ski track to the summer trailhead. 

The trail had a few inches of fluffy dry powder on top of very hard crust so we just walked in boots for the first 2.5 miles or so (from the car). At some point I put microspikes on because I got tired of bracing for slipping. My friend continued just in boots. The trail is very mellow and pretty flat winding throughthe trees with on and off river views. There are a few trees down but they were easy to pass. At that time the trail was very easy to spot, it makes a deep V in the ground so easy to see even though there were no human tracks. There was a set of coyote prints that continued mostly on the trail the whole way. 

We walked 4.25 miles to a lovely spot in the sun right next to the river. At that point I realized we were off trail a little when I saw pink flagging tape through the trees. It would be very easy to get back on the trail by walking between trees, no bushwacking needed. If you end up following our prints and then they stop at a nice spot by the river, look for a pink flag to the right. Also, GPS showed we were slightly off trail. 

We chose to turn around there and not go all the way to the lake. That would have been 10 or 10.5 miles round trip (including walking on the cross country ski trail).

Snowmobile trail parallels the hiking trail on the other side of the river. You can hear them but it's not terrible and we didn't smell any exhaust. 

The river is lovely and pretty. We put on snowshoes at about 2.5  or 3 miles when the snow gotten a little deeper and we got tired of plowing through ankle deep powder. 

You can get 4 or 4.5 miles round trip on this trail before crossing any avalanche terrain. After about 2 miles, the trail traverses a fairly steep tree covered slope, 25-35 degree angle. I wouldn't do it on a high avalanche danger day. 

Overall, we did 8.5 miles on a cold Saturday (13F in the morning!). 

Glad we stuck it out. When my group arrived today we almost turned around because of the rain/snow mix, but just a few miles in it switched to light snow. About 33 degrees. 
Route 903 had some snow/ice patches along the way but not too bad and they maintain the roads well. But the trailhead parking lot is closed to vehicles, only snowmobiles could enter. 
Word of caution! Be super careful where you park because they (wrongfully) issued expensive parking tickets in the area. And be sure to bring your pass. 
The trail itself is not super hard as elevation gain is low, however it’s a long trek. A total of 10 miles round trip, took us about 5 hours to complete with all the ups and downs and lots of pics. There was a huge tree down that you’ll have to crawl under and a few areas that were very narrow for snowshoes on the slick steep edges along the ridge. I fell a few times. Snow was mostly compact. 
The best views of the river started around mile 3.75. Did not see any wildlife, only rabbit prints. 

Had high aspirations of going to Cooper River snowshoe trail today … chose a lower elevation spot due to considerable avalanche risk as well as the cold and wind …
fatigue from trail breaking and super cold temps (for me!) had me turn back just after I actually got to the Cooper river TH, but a super pretty location nonetheless!

Started around 11:00 at Salmon la sac sno park. Correct if I’m wrong here, but it looks like you could park 0.25 miles closer to the salmon la sac GC still within sno park area. Signs say “Begin parking here” and a Sno Park sign on the road about 0.25 miles closer than where the usual sno park is …. I parked on sls road near the snow park along w/ 2-3 snowmobile trucks. . No need for high clearance at this time, just traction

0.5-0.75 along sls road to start of unplowed area. It’s still very packed snow at that point too - snowmobiles doing the work based on the tracks. Then the SLS CG branch separates and it was breaking trail from there on out … prob 12” of fresh stuff. I think I was overdressed bc I was sweating and taking breaks more often than usual … hard work.
Anyway - lots of quiet, sunny and filtered light into a snowy forest. The cle elum and cooper rivers were gorgeous technicolor pastel light blue w pillowy snowy rocks on the banks …
Finally made it to SLS TH proper and was already pretty tired… made it another 0.5 miles along Cooper river trail (totally covered - making trail on the most likely path- some evidence of prior snowshoers I would guess)
I turned back and did a loop around SLS CG and made my way back to the road on a side spur …
Spent some time back at the Cle Elum river to take pictures and enjoy the scenery on a sweet little snow covered bench.
Overall very picturesque, cold as … really cold stuff
Gotta lower my expectations when it’s so cold and deep I guess!
Prob ~4 miles, minimal elevation

We got to the Salmon La Sac Sno-Park around 10am. The main Sno-Park lot had not been plowed that day and was a little deeper than we wanted to venture into so we found parking along 903/Salmon La Sac Rd and walked 2/3 of a mile to the bridge across the Cle Elum river and the start of the un-plowed non-motorized portion of the trial system. The non-motorized trials hat not yet been groomed but a Foresty Ranger we ran into said they were going to start grooming operations within the next week. We continued down the road bed towards the Salmon La Sac trailhead and broke trail on top of an older snowshoe track that was visible but under a good bit of fresh snow. We went another 1/2 mile past the trailhead marker along the Cooper River Trail, had lunch and sat by the river a while before heading back to the car. 

We only crossed paths with one other pair of snowshoers and one other snowmobile on the way to the trail head. The Ranger that we talked to on the way out did remind us that if you are going all the way up the Cooper River Trail to Cooper Lake there is a notable avalanche shute with a runout that encompases the Cooper River Trail so be avalanche aware if traveling that area. An alternative with less avalanche exposure would be to snowshoe on NF-46 on the other side of the river to reach the lake but you would have to share the road with snowmobiles. 

Today we snowshoed the Cooper River Road for about 4 miles RT. This makes a good, easy outing on a wide road that gets snowmobiled enough to break trail but not too much. We saw just 5 machines today, all of the riders friendly and respectful of us slow muscle-powered folks. The grade is gently uphill in this road for the first 3 miles. I know that from biking it in the summer for the past almost 50 years. After this long hill, it rolls up and down for a couple of more miles to the Cooper Lk turnoff. The scenery was spectacularly wintery and beautiful. This makes a good trip for all abilities, and we do it and other local roads up the Cle Elum Valley every year.