Cave layout is kind of confusing. I give coordinates for Val'sharra, though as soon as you enter, some addons might report coordinates for the Lifespring Cavern, which is a different coordinate system entirely. Hopefully you can make out what I mean by descriptions.
Cave entrance is at at 38.4, 61.3 in Val'sharra. (Note: All map coordinates are given for Val'sharra's map; some addons show coordinates for the cave's map). Follow the corridor in, and there's a small pooling of water with a dirt ramp up to the left (northwest). That leads to the first puddle where there's a path up four rocks to the left (southwest). That leads you at another puddle at 37, 59, which has a path upwards with half-buried wooden logs that goes south (even though the mob is north). Go up that, then at the top (36.6, 59.8), turn right to take another half-buried-log path up, which curves up north to 41.4, 67.6. From there you should see Gelmogg's spawn point around 35.5, 57.1.
You can turn the quest into [npc=99533] right there, completing the first chapter in Val'sharra's main story line.
Also, you may have noticed an unreachable [object=244519] above your head when you were killing mobs down below near the first puddle. From this top level near Gelmogg, you can follow a path down some wooden steps that start at at 37.9, 58.2, and curves down to the treasure chest at 37.1, 57.1.