Yakima has an area locally called Ahtanum Meadows. It's DNR land, with Parks recreation lot, requiring a sno-part permit. From I-90, head sound on I-82 to Yakima. In the Yakima area, take the Union Gap exit. You'll have to dog-leg it around a couple blocks to get on Antanum road. Go on Antanum road for about 24 miles. Around there will be a fork, with a store, just stay to the right. Go about another 4-5 miles to the camp area, called Ahtanum Meadows. The maps are enlargeable for one with high-speed connections. Remember you'll need a sno-part permit and possibly tabs on your sleds.
If you need additional information vist the direct link to Washington State's Parks-for that Region.
We usually decide on a 2-way radio channel to contact on, should we get separated.