You can either take Elliot Rd. east til you see Mountain road, take a right, (its a ways down) start going south til you see the factory and you should see a gap in the fence with obvious signs of vehicles having been there and just follow the tracks to the field.
Or you can take Ray Rd. or Elliot Rd. til Ellsworth, make a right on Ellsworth, go south on Ellsworth to Pecos, take a left and head east on Pecos til you get to Mountain rd, take a left and drive a little North of the factory til you see the gap in the fence.
I think theres another way to get to the field from some Western entrance but idk.