Black Hills Mining Museum The "Girl" is the centerpiece of the Museum and is marked by a 100 foot high steel headframe. Once mined to a depth of 3200 ft, she produced silver, lead and zinc from 1875 till 1956. Common Mistakes In Confined Spaces Monitoring These include thermal, http://2-031246.blogstival.com/26667631/common-mistakes-in-confined-space-monitoring