Sometimes, but definitely not always.
Deserts can be any shape. Take Death Valley for instance, home to the highest air temperature ever recorded. They say a picture is worth a thousand words. Well, these are my own photos, featuring my wife because she’s the better looking of the two of us. :)
Looks pretty mountainous to me. Even the sign’s artist recognizes that.
Death Valley’s mountains are some of the most hostile in the world.
Badwater Basin, the lowest point in N. America and the hottest place on the continent. Sure, it’s flat here, but it’s not very wide and those slopes aren’t much cooler or wetter.
Those are some forbidding mountains (my car in the foreground). Also, I find this photo really messes with my equilibrium if I stare at it long enough.
If you want to know how hot this canyon is, turn your oven on, wait 20 minutes and then stick your head inside.
My final photo. Stragglers in the Badwater Ultramarathon, the most grueling race on Earth. It is 135 miles and includes a cumulative 13,000 feet of uphill running. Those poor bastards wish this place was flat.