Wendy and I just got back from our vacation to the Southwest US.  In a sentence, we went to the Grand Canyon, Bryce Canyon National Park, Zion National Park, and Death Valley National Park, slept in a tent 6 out of 8 nights, drove 1500 miles, took lots of pictures, and had a great time.  Pictures are here.  More details follow. 

Summary
Day 1 - Clear and in the 90s; flew into Las Vegas; stocked up on food and supplies; grabbed dinner at Mr. D'z Route 66 Diner in Kingman, AZ; camped in the Kaibab National Forest outside Grand Canyon National Park, where the temperature got down in the 40s at night

Day 2 - Clear and in the 80s; drove into Grand Canyon very early; hiked to Cedar Ridge along the South Kaibab Trail with an informative park ranger (3 miles); strolled along the Rim Trail; got a prickly pear margarita at El Tovar Hotel (too alcohol-y); showered at Mather Campground; watched the sunset at Powell Point; camped in the Kaibab National Forest again

Day 3 - Clear and in the 90s; climbed the Desert View Watchtower on the way out of the park; stopped off at the Little Colorado River Gorge; briefly walked around in Coral Pink Sand Dunes State Park; arrived at Bryce and looked around a bit; camped in Dixie National Forest, where the temperature got down in the 50s at night

Day 4 - Perfectly clear and in the 80s; got up to see the sunrise in Bryce (wasn't that good); hiked the Navajo/Peekaboo/Queens Garden Trails (6.4 miles); got lunch at the Bryce Canyon Lodge; drove to nearby Mossy Cave and walked around in the river; hiked the Bristlecone Loop Trail (9100 feet elevation) and played in the snow; showered at the general store; stopped at a few more spots on the way out of the park; camped in Dixie National Forest again, where it was windy and a little wet

Day 5 - Cloudy and in the 60s; drove to Zion; got lunch at Zion Lodge; hiked to the Lower Emerald Pool in the rain; rode Fuzzy the horse and Moses the mule; hiked the Riverside Walk just up to the Narrows (water was too high); stopped off at Big Bend; hiked to the Weeping Rock after going a half mile in the wrong direction (uphill); spent the night in Terrace Brook Lodge

Day 6 - Pretty clear and in the 60s; hiked to Angels Landing (5 miles, 1488-foot climb); stopped at the excellent Springdale Fruit Company for lunch on the way out of the park; drove to Death Valley; stopped at Zabriskie Point for some desert views; camped at Furnace Creek (196 feet below sea level), where the temperature stayed in the 70s all night

Day 7 - Hazy and in the 80s; drove to Badwater Basin (282 feet below sea level); hiked to Natural Bridge; saw weird salt crystal formations at the Devil's Golf Course; looked at colorful desert minerals on Artists Drive; hiked up Mosaic Canyon; walked around the Mesquite Sand Dunes in the rain (yes it rained in the driest place in the country); stopped at Dantes View on the way out of the park; drove to Red Rock Canyon National Conservation Area just outside Las Vegas and camped, where it was cold and rainy

Day 8 - Cloudy and in the 70s; drove into Las Vegas; checked into the hotel early (yay!); packed our bags

Quick facts
Miles driven:  About 1500
Highest elevation reached:  About 9300 feet
Lowest elevation reached:  -282 feet
Highest temperature experienced:  90s
Lowest temperature experienced:  40s
States visited:  4 (Nevada, Arizona, Utah, California)
Showers taken:  6
Pennies pressed:  4
Miles hiked:  About 25
Times coyotes were heard at night:  2
Times we wished we were doing something else:  0

Thoughts
Two important things for the trip were health and weather.  It occurred to me about a week before we left that our trip would change significantly if either one of us was injured or hurt with something as simple as a twisted ankle.  Thankfully we were both in great health before we left so it wasn't an issue.  Weather was also pretty important, but I didn't expect much bad weather considering the fact that the areas we were visiting were deserts with very little rainfall.  However, it rained for roughly half the trip, which turned out to be a pretty big downer, especially since so much of the trip was about enjoying an outdoor experience.  But as long as you have a poncho and some relatively warm clothes, rain doesn't stop much.  It definitely would've stopped our harrowing ascent up the slippery rocks and steep cliffs of Angels Landing in Zion, but most other things would have and did happen as planned. 

If I was gonna do the whole thing over again, one small thing I would change would be water storage.  We thankfully packed more than we needed to with bottles and a huge collapsible container.  It might've been slightly easier to just buy several 1-gallon jugs of water when we got there and filled up smaller bottles of water for use when hiking.  But that's a small thing.  No harm, no foul.