Although >90 kimberlite diatremes have been found in the area, it was not until after 1963 that these bodies were correctly identified. The presence of large inclusions of sedimentary rocks had hindered their recognition. In 1975 a diamond crystal <1 mm was accidently discovered while thin-sections were being made of rock from the Shaffer 3 body in Albany County, Wyoming. Subsequently additional diamonds from other localities in the area were identified. The diamonds usually range 0.2-2.0 mm (a few >3.5 carats). They are usually colourless, but light-brown, blue-white, pale orange, pale to bright yellow and nearly black crystals occur. Associated minerals, including chrome-diopside, chromite, magnesian ilmenite, pyrope and omphacite, are described.-R.S.M.