I'm traveling to the states for the first time over December/Jan and i currently have zero plans! Main aim is to do lots of climbing (mainly trad but sport is also cool). Also keen on canyoneering, kayaking, mountain biking - anything really! I don't know anyone in the states so advice would also be great :)
It could be really nice in Utah in Dec/Jan, but it also likely could be really cold for climbing. Perhaps consider traveling somewhere warmer? Check out Cochise Stronghold or Joshua Tree National Park.