Need to look at Utah's budget, sounds like traffic enforcement based on revenue production not public safety. The California plates probably played a roll too
SERIOUS WARNING- Wish I'd remembered to warn you before you left, DO NOT SPEED IN A NATIONAL PARK. A ticket from a park ranger is a federal bust, very expensive and the rangers are ruthless. Not sure if you remember your aunt getting popped in a Yosemite speed trap for doing less than 5 mph over (she wasn't), it cost her a bundle and ruined a great day. Know your speedo and set the cruise for at least 3 mph under to be safe.