Black-footed ferrets (Mustela nigripes) excavate subsoil from black-tailed prairie dog (Cynomys ludovicianus) burrows and deposit it in unique piles. Black-tailed prairie dogs tend to fill in or "plug" burrows visited or occupied by ferrets (Hillman 1968, Henderson et al. 1969, Fortenbery 1972). In this paper, we describe the configuration, rate of production, persistence, and seasonality of ferret diggings and rate of burrow plugging by prairie dogs within white-tailed prairie dog (C. leucurus) colonies. Published in Journal of Wildlife Management, volume 48, issue 4, on pages 1441 - 1444, in 1984.