The foundation, which opposed the Bureau of Land Management muster, has provided an update on the horses released back into the wilderness.
It reported that the most famous of the horses, the stallion Cloud, is lame.
The foundation's report came on the same day that the 57 horses retained by the bureau went under the hammer in Lovell, Wyoming.
Foundation voluntary director Ginger Kathrens, whose documentaries made the Pryor Mountain herd famous, said the horses left on the range are "clearly damaged".
"We were up on the mountaintop yesterday and the cruelty of this massive roundup has not faded away," she says.
"Cloud is lame on his right front and his daughter is still extremely sore. It was painful just watching them walk to water."
One of Cloud's mares, also injured, appears to have a possible stifle injury. His four-year-old daughter, Firestorm, has significant difficulty walking at all.
"I think they will recover but it is hard to know and winter is just around the corner," Kathrens says.
In the past 15 years, all roundups in the Pryor Mountain Wild Horse Range have occurred later in the year when the horses were lower down on the range.
The roundup, she says, took place in early September when nearly all the mountain horses were the furthest away possible from the trap site.
Foals less than one-month-old were forced to run over 12 miles along with their families to the bureau's corrals at the base of the mountain.