From Toronto in mid September to Quebec City in late September, hypothetically you really could encounter everything from shorts-and-sunscreen weather to boots-and-jacket weather.
The driving distance between Denver, CO and Salt Lake City, UT is 536 miles. The driving time would be approximately 8 hours 30 minutes if driving non-stop in good conditions.
Driving Distance from Billings, Montana to Yellowstone: 205 Miles. Driving Distance from Missoula, Montana to Yellowstone: 315 Miles. Driving Distance from Boise, Idaho to Yellowstone: 450 Miles. Driving Distance from Salt Lake City, Utah to Yellowstone: 370 Miles. Driving Distance from Cheyenne, Wyoming to Yellowstone: 500 Miles. Driving Distance from Denver, Colorado to Yellowstone: 750 Miles. Driving Distance from Chicago, Illinois to Yellowstone: 1,450 Miles. Driving Distance from San Francisco, California to Yellowstone: 990 Miles.