Tri-State Mining District
Image source: Tulsa District Library Document Information,
Picher Mining Field, Northeast Oklahoma, Subsidence Evaluation,
website: http://www.swt.usace.army.mil/library/TAR%20CREEK%20SUBSIDENCE/FIGURES/FIGURE%202.1.PDF
From the early 1900's to the 1960's the Tri-State Mining District was mined extensively for lead, zinc and cadmium. During the 1970's, mining operations ceased and mines were subsequently abandoned so tailings and shafts remained throughout the region.
Rain run-off flowing across the ground surface falls into the numerous mine shafts filling the open tunnel spaces beneath the surface. Standing water accumulates heavy metal left in the mines. From there it travels into the upper ground water aquifers, contaminating drinking water supplies.