It's probably best if you come to Pindale, Wyoming for your snowmobile adventure sometime between January and the middle of April. This is when you'll find temperatures are the most agreeable for getting out in that white landscape. However, anytime from early December to mid April will work.
The terrain around Pinedale varies from gentle rolling prairie to rugged mountain forests. It makes for some exciting snowmobiling. Many of the trails will go as high as 10,000 feet. You can rent equipment in town or even hire on a guide. One of the most popular trails is the Continental Divide Snowmobile Trail, going right through town. There are 250 miles of marked trails all through the Wind River Mountains, offering some great riding and incredible views of the surrounding backcountry. With miles of beautiful scenery and snow as much as six feet deep or deeper, you can't beat the Pinedale area for some perfect snowmobiling.