Dan---The fence was useless in stopping the stampede.
exzim---The fence was installed (I presume) by the National Park Service to keep grazing cattle from entering the park. The adjacent land is managed by the Bureau of Land Management, which allows grazing on certain tracts of its land. In some places (Jug Rock, for example) one can see hoofprints and dung. Sorry for the two-year delay in answering your question. :-(