As you head up into the entrance of the Desert Resort, a sandstorm will begin- this sandstorm is constant, and it does affect your battles, so watch out for Rock and Ground types with improved special defense, and things that use Sand Rush, Sand Veil, or Sand Force (which thankfully are usually Ground types themselves... usually). 

In addition to Sandile, Darumaka, Crustle, and Scrafty, this sand includes the Grass-type Maractus, whose massive Special Attack stat is thankfully only useful for its Mega Drain attack at this level.  They also have Pin Missile, but that’s usually not an issue unless you’re unwilling to switch Pokemon ever.  Lucky trainers can also run into Sandshrew here, which are an interesting throwback all the way to the original Pokemon games.  These tough little things are mostly dangerous for their high Defense and Sand Veil- so a good Special Attack move will usually wipe them out (if it’s not electric).  Levels vary a bit around here, but overall you shouldn’t see anything higher than 21 or lower than 18 in the sand here. 

If you badly need a Grass pokemon, Maractus will do, but its defenses are poor and so is its speed unless it’s got Chlorophyll and sunny weather, so this shouldn’t be a prime choice progressing through the game.  Sandslash, on the other hand, is a tough-as-nails physical fighter with access to a lot of high critical ratio attacks and a few neat status effects, as well as Swords Dance.  While it’s largely outclassed by Excadrill, if you prefer Sandslash you can use that instead for pretty much the same effect, just on a slightly lower scale and less abusably.

You’ll hang a left, then pass a couple of guys just hanging out and getting their faces ground off by the sand (why?).  They’ll mention that the Desert Resort is a great place for training Pokemon, and the existence of the Relic Castle, which is apparently also pretty cool.

Past them is an especially large pit of encounterful sand, and the gate that leads into the Desert Resort itself.

A kid in the gateway will point out that pale sand is safe from encounters just in case you’d missed it, but other than that there’s nothing to see here.