Zion National Park in Utah is one of the most amazing National Parks in Utah! It gets so busy in the park that by the end of March they only allow shuttles to drive through the park (until Labor Day). I ended up signing up for the Zion Half Marathon (it was held in the middle of March in 2015), so we were able to drive through the park! We also ended up camping right in Zion, which I HIGHLY recommend. It isn't a super dog-friendly National Park, so we didn't do as much as hiking as originally planned, but the warm weather was a great change from the still very snowy Steamboat. I'd recommend planning to visit the park during the Spring or Fall, when you are able to drive-through and crowds are minimal. The trees were already blossoming when we visited, so it did feel very Spring-like in mid-March (ice cream cones were also a huge bonus). Make sure to plan your trip early and highlight some of the must-see canyons/ hikes. It's great to have a plan of what you really want to do, but have a loose schedule for doing them!