Reference quads for emergency response reconnaissance developed for use by the US Environmental Protection Agency. Grid cells are based on densification of the USGS Quarterquad (1:12,000 scale or 12K) grids for the continental United States, Alaska, Hawaii and Puerto Rico and are roughly equivalent to 1:6000 scale (6K) quadrangles approximately 2 miles long on each side. Note: This data set is available as a national-scale file (>80MB) and as individual regional subsets. Each regional extract includes a 20 mile buffer of tiles around each EPA Region. The URLs for each are as follows: Entire Country: https://edg.epa.gov/data/Public/OLEM/OLEM-OEM/6kquads_epa.zip, Regional subsets: https://edg.epa.gov/data/Public/OLEM/OLEM-OEM/6kquadr[enter region number].zip (e.g., R6 subset URL https://edg.epa.gov/data/Public/OLEM/OLEM-OEM/6kquadr6.zip)