There are three resorts in the US that don't allow snowboarders: Mad River Glen in Vermont and Alta and Deer Valley in Utah. Alta is somewhat of a throwback in time. Lots of die-hard skiiers who don't want change.
Deer Valley is known for their grooming, their customer service and their food. Deer Valley limits their ticket sales. That's not all that unusual, and I'm not sure if it's urban legend or not, but supposedly the limit is not based on uphill lift capacity, but rather the capacity of their on-slope restaurants.
They survey their customers extensively and every year or so, and the customers resoundingly do not want snowboarders. But Deer Valley is also OMG expensive. My recommendation for visitors is Solitude. I've never had a bad experience there. Being on the west side of the Wasatch Mountains they get more snow than the resorts in Park City.
About two years ago Deer Valley bought Solitude. Then Deer Valley was sold, though the former Deer Valley owners kept ownership of Solitude.
If you're coming to Utah to go skiing and/or snowboarding I definitely recommend Solitude. If you're a skier, I also recommend Alta for the experience. And though it's out of the way, I'd also suggest Snowbasin. During the 2002 Olympics the steep events were at Snowbasin: Downhill, Super-G, Giant Slalom and Slalom. One downside of Snowbasin is there is no night-life close by, or on-mountain lodging