You must remember that November to January is the middle of winter in the USA. The climate can vary considerably from location to location depending how far north you travel and at what elevation you travel.
Here is a brief explanation of the typical winter weather in the west.
The California Coast has mild winters due to the influence of the Pacific Ocean. Los Angeles and San Diego are in the southern part of the state and the weather can be anywhere from cool to cold, but you will not get snow or freezing termperatures. San Francisco is nearly 500 miles further north, so you can get colder temperatures but still no snow or freezing weather. In the mountains near Yosemite and Kings Canyon you will find both freezing temperatures and snow. At the higher elevations, you will find lots of snow, enough to close some of the roads and mountain passes from November until May. East of the Mountains, in the rain shadow desert, you will find termperatures that vary according to altitude but very little snow. Death Valley is actually quite pleasant in the winter when the oppressive heat is gone.
Montana can be bitterly cold in the winter with the possibility of significant snowfall. Tourist would likely avoid Montana during the winter months unless they ski. Yellowstone Park is closed to vehicles during the winter but they do allow a limited number of snowmobiles and cross country skiers in, plus they have snow cat busses to take tourists to some of the attractions.
Denver Colorado is situated on the plains in the rain shadow of the Rocky Mountains. The temperatures can get below freezing and it can snow, but it does not typically receive large amounts of snow. Unfortunately, the best scenery is located in the Rocky Mountains west of Denver where you typically find significant amounts of snow. It is great ski country, and they try to keep the main roads open to the ski resorts, but some of the passes and mountain roads are likely to be closed.
As for accommodations, I have traveled in the UK and Europe where B&Bs or farmhouse gites are a great alternative to hotels. That is not as viable of an option in the USA. In the USA, B&Bs tend to be quaint, lovely and typically more expensive than hotels. Vacation cabins are available to rent near some of the national parks and attractions or near the tourist beaches, but not elsewhere.
If you really have your heart set on seeing Montana or Colorado, and you are not a skier, I suggest you consider visiting during the summer months.