"Goomalling"! That raised my curiosity antenna!
I'd heard of Geo-caching, and Paintballing and thought this sounded like the latest craze.
Turns out it's a weird WA place name!
At least a lot of WA place names are unique in Oz, unlike so many duplicates on the east coast.
Basically, think up a syllable or two and put "up" on the end and you're set.