As promised, here’s a description of the Carrion Canyon Treasure Room. One the party has tracked down the four elemental keys, they are able to open the door. What they find there is not pretty.
The dwarves who built the Carrion Canyon fortification did not do any smithing or enchanting there, it was primarily a staging point for their campaigns in the White Mountains and a way station for transporting exotic items captured there. When the dwarves abandoned the fort, they left certain live eggs in the Treasure Room. Depending on the level in the party, eggs will have hatched that produce an appropriately difficult encounter for the party. This could be any number of Giant Spiders, Giant Scorpions, or Giant Snakes (though Giant Spiders make the most sense for the region).
For higher level parties, it may be appropriate for there to be one or more dragons in the treasure room (preferably not incorporeal or digging dragons). Given the confined space, these dragons must be under 100 years old or have their growth stunted.
With the enemy defeated, the players will find very mixed treasure. It could be everything from additional unhatched eggs to giantish weapons to artifacts of Chitalin to coins and gems. Really, anything could have ended up in this vault.