The Rio de las Vacas heads within the San Pedro Parks Wilderness where it is a very small stream full of native Rio Grande Cutthroat Trout. As it crosses Sr126 it grows in size and meanders south and west through a beautiful meadow. It is this section that is most popular and is stocked with catchable sized Rainbow Trout. There a lots of Brown Trout to be found in this section and on south as it joins with the Rio Cebolla at Porter Landing to form the Rio Guadalupe. A large section above Porter Landing is private land, including the Chaparral Girlscout Camp.