A note about the black specks on the soles: there was a warmup lane on the inside of Stevenson Track, the main track at Hayward Field that was notoriously hard - and hard on the legs. The warmup lane was a refuge for tired legs. 

It can be seen in my photograph of Frank Shorter and Steve Prefontaine: Prefontaine #1. They are warming down on the soft surface and not on Stevenson track after their May 29, 1975, 5,000m race.