This feature class depicts Comstock-era mill locations within the Carson River Mercury Site (CRMS). These locations were obtained in order to define the investigation area boundaries of Operable Unit 1 (OU1) within CRMS. Completion of this dataset took place over several years and phases, as described below.

EPA survey: The first mill survey took place in 1993 by EPA, contracted by Piedmont Engineering.113 mills were identified in this survey. Later, Nevada Division of Environmental Protection (NDEP) conducted historic research on Comstock-era mills to expand upon this dataset, identifying an additional 87 mill sites, bringing the total number of mills in the dataset to 200. This process is described below.

NDEP Historical Research: Mill site locations were determined based on georeferenced maps procured from the EPA, NDEP, Storey County and the UNR digital map library. All maps were georeferenced based on available landmarks by heads-up digitizing techniques. The maps utilized had varying degrees of accuracy based on their date of production. Some maps utilized dated back to the 1860's. Once all historic maps were scanned, imported and georeferenced, all map sources were evaluated and mill site locations were digitized based on the preponderance of evidence (by comparing mill locations as shown on the various source maps) to determine each mill's location.

A vector layer of mill sites was thus constructed using georeferenced raster layer resources. This layer of mill sites contains the locations of 188 historic Comstock Era mills as well as 12 additional tailings locations that are not directly associated with a mill site. 33 additional sites were identified; these consisted of sites that were known to exist but not located on historic maps, as well as cyanide mills.

Broadbent and Associates, Inc. field surveys: In 2012 NDEP contracted Broadbent and Associates, Inc. to survey all mill sites defined in this dataset. The contractor successfully verified the remains and evidence of 73 mills. Inconclusive mill evidence was found for 98 of the sites in the dataset. For 65 mill sites, the contractor was not given permission by the landowner to access the property and therefore the mill site location was not surveyed. Survey status is unknown for 1 mill.

The contractor provided a feature class of all 236 mills accompanied by a detailed report on their survey efforts, listed below: Broadbent and Associates, Inc., Eric M. Seitz, Project Manager. January 31, 2013, Final Report – Comstock Archaeological Mill Site Inventory, Unpublished.

NDEP reviewed this report and the associated feature class to confirm each mill point location and provide attribute information on the survey status of each mill site. NDEP added the attrtibute field "Field Verified" to provide information on the field verification status of each site. A value of "No" indicates the site was not surveyed in the field. This was due to to access limitations and denials for sites located on private property. A value of "Yes" indicates the site was surveyed and evidence of the mill was found. A value of "Surveyed" indicates the site was surveyed but inconclusive or little evidence of a mill was found.