The Moab area, including the Arches and Canyonlands National Parks are real harsh deserts where water is rare and hard to be found. ALWAYS take water with you!! Even for a short walk! On a hot day, you need at least one gallon (4 liters) of water a day.
Sun cream, hat and long light-colored sleeves are also a good idea to protect yourself from the harsh sun in the summer.
The beauty of the Moab area has its downside: it attracts A LOT of people! Especially Arches National Park, and the Iskand in the Sky district of Canyonlands National Park attract millions of visitors. The high season is September and May. Note that as soon as you walk more than one hour (or even half an hour) away from a parking lot, you will loose 99% of the crowd.
The most popular spots are the Delicate Arch in Arches NP, especially at sunset as all guidebooks tell you "go see Delicate Arch at sunset", so all the sheeps go (see picture). Also popular is Devil's Garden trail in Arches NP, but 75% of the people stop half way at Landscape Arch where the trail becomes slightly more difficult (you have to walk on slickrock, oh la la!).
Moab is at a lower elevation than most areas in the region. This means that this is also gets hotter here. The temperature was approaching 100 degrees the day I was there. The sun is also very very strong.
Expect hot summers. Average high temperatures for May and September are in the 80's, June and August average temperatures are in the high 90's, and July averages 100. Dehydration can be a real problem, carry lots of water during your explorations if visiting in these summer months
If you decide to mountain bike, hike, etc on the trails make sure you have a map and are well hydrated. Bring extra water with you. People get lost every year on the trails since the places are very remote and dangerous, especially if you get lost because a lot of times no one knows you are gone.
Swimming or bathing in the Colorado River is very risky. The currents appear tame but are actually quite swift. People have drowned when they were swept away downstream. The only time you should attempt a dip at all is if you are on a rafting trip and have a life preserver on. Rafting guides often give you the option to jump in where they know the river to be safe enough. They will also be keeping an eye on you should you run into any trouble.
When in the Moab area, take care of yourself and your vehicle, by being quite aware of the terrain, the difficulty of the trails you are driving. ALSO, take care of the environment by only driving on established roads and trails, pack out all trash, and leave nothing! Thanks
You can be fined for litering in the National Parks. Also, you are not to take any rocks or remove items form the parks too.
Cloud to ground lighting strikes are common during the summer months. Be careful and keep an eye on the sky!
These are a couple of pictures I saw of what can happen out there in the country. These are more than likely rentals, so who cares?
Be prepared for hiking in the park. One should have plenty or fluids with them (not in the car- like I did) and sunscreen. I was not properly perpared!!
It can be really hot here in the summers, so make sure you drink alot of water while visiting the National Park.