Ha! So glad to see that Lopov has taken a sneaky peek here. His knowledge of NV is very good.
Yes, what you are looking at is the Sulphur Cave, but it is not the one under Vault 19. The game actually has a second location of sulfur deposit in the game, except that this one is non-explosive. The quest that sends you there is the quest to acquire Dinner Bell, one very good shot gun. You have to find some Fire Gecko eggs in the 'Bleed me Dry' quest.
The cave is called 'Bootjack Cavern.'
So Lopov has the win for being oh so close.
Your turn!