Spawn and kill Chief Strongarm ( 36, -26, 60 ) /waypoint 36, -26, 60 and mine the rock that appears.
Clear the seven groups of ruffians (in three sets on the second floor). This will start a ring event and spawn three groups of summoners who will begin casting a spell. After killing the three groups of summoners, Chief appears (untargettable) and summons four mudrakers. After killing those, Chief becomes targetable.
Spawn and kill Lureclaw the Angler and Gulp ( 56, -41, 121 ) /waypoint 56, -41, 121 and mine the rock that appears.
In the lower water area, near where you fall if you drop down the waterfall at ( 54, 0, 101 ) /waypoint 54, 0, 101, clear all the netslingers and other grinnins in the area. This will spawn a new wave of mobs. Kill them. Your rock will spawn on the land near by.