Head to McQuibble's Farmhouse ( -1857, -25, -210 ) /waypoint -1857, -25, -210, you will get an automatic update upon entering.
Run over the three farm fields to the southwest of the farmhouse looking for patchs of soil. Find and click on a small pile of soil to advance the quest. (looks like a small anthill)
some are reported around:
( -1742, -2, -169 ) /waypoint -1742, -2, -169
( -1763, -2, -87 ) /waypoint -1763, -2, -87
( -1703, -2, -81 ) /waypoint -1703, -2, -81
( -1695, -2, -68 ) /waypoint -1695, -2, -68.
Run over the two farm fields to the northeast of the farmhouse, again looking for soil patches.