In a food processor, combine the salt, pepper, garlic cloves, rosemary and chile powder and process until fine. Add the olive oil and pulse to form a paste.
Place the prime rib roast on a cutting board, bone-side up and rub with 1 tablespoon of the salt paste.
Transfer the meat to a large roasting pan and pack the salt paste all over the fatty surface, pressing to help it adhere. Let the prime rib stand at room temperature for 1 hour.
When ready to cook, start the Traeger on Smoke, lid open, until a fire is established (4 to 5 minutes). Increase the temperature to 450°F and preheat, lid closed, for 10 to 15 minutes.
Roast the prime rib for 1 hour, or until the crust is slightly darkened. Lower the Traeger temperature to 300°F and roast for about 2 hours and 15 minutes longer, or until an instant-read thermometer inserted into the center of the roast (not touching the bone) registers 135°F.
Transfer the roast to a large carving board and let the meat rest for 30 minutes.
Carefully lift the salt crust off the meat and transfer to a bowl. Brush away any excess salt.
To remove the roast in one piece while keeping the rib rack intact, run a long sharp carving knife along the bones, using them as your guide. Leave on 1/2 inch of meat, more if reserving for leftovers.
Carve the prime rib roast 1/2 inch thick and serve, passing some of the crumbled salt crust as a condiment.