The grazing grounds is a place just outside Klamath
This field is where Torr Buckner's brahmin usually graze. There is a small shack on the path back into town, which contains a pair of radscorpion limbs.
During the Guard the brahmin quest, there will be a large group of radscorpions in the South East corner of the map for Chosen One to vanquish.
The grazing grounds appear only in Fallout 2.