The National Parks have some of the great trail hikes.  The key is to go when no one else is there, which means: not summer.  Watch the weather maps and spot a window of opportunity for a pleasant, un-crowded hike.  Winters in Zion National Park are often mild with 60 degree daytime temperatures possible.  DayHiker has hiked this majestic red canyon the past two winters around Jan 1, found the weather great and the accommodations (Desert Pearl Inn, Springdale) upscale.