Before the dark portal Gnomeregan was a very peaceful place. Each gnome had a job and a role and they did their part to keep they city as a whole working at maximum efficiency.
The techniques utilized by current gnome “shadow” priests were developed for use by members of the Gnomeregan Geo-architects. These gnome Dowsers excelled in scouting out new paths for tunnels to expand Gnomeregan ever deeper in to the heart of Azeroth.
The skill set used was rare among gnomes for a long time. Few could master the arts of ‘sensing’ what was deep under the terrain. Combine that with the dangers inherent in being the first to explore newly excavated tunnels and you can imagine how few and far between these gnomes were.
The Cataclysm compromised the integrity of the whole city in one way or another, and so a call was put out and many more gnomes began to learn these esoteric arts.
Here is a picture of me giving it a shot. I could hear the call from the darkness of the earth, but I felt that gnomes future was on the surface among the taller races, not hiding in the darkness.