The Topia Mining District lies in northwestern Durango State at coordinates 25± I I'N and 106±33'W, 50 km from the Sinaloa-Durango state line and 100 km east of Culiacan. Sinaloa (Fig. 1 ). It occupies the physiographic transition between the Volcanic Highlands and the Barrancas Zone subprovinces of the Sierra Madre Occidental Province. Access to the district is by land and air. Commercial airlines fly to Topia from Durango and from Culiacan (Sinaloa). The Durango-Topia road runs for 390 km; the first 180 km, to Santiago Papasquiaro, are paved. Topia is equipped with municipal public services and schools to high-school level.