What we know
Post office 1885-1896 on Running (Box Elder) Creek north of Elizabeth; Scott dates it 1884.
Where it was
'Orsburn P.O. 1884': Scott, Historic Trail Map of the Denver 1x2 Quadrangle (USGS I-2639, 1999, S-0106), symbol read from the reprojected sheet (good to a few hundred feet). Place Names of Colorado: Sec. 7, T7S R64W, 'Rural Post Office 1885-1896. 7 mi N of Elizabeth.'; this point is 0.64 mile from that section's center.
Read from Glenn R. Scott's USGS historic trail map of 1999 and confirmed by a second, independent source.
Sources
Sources are named in the text above. Numbers such as S-0080 refer to our source list. Most newspaper quotations were read in the Colorado Historic Newspapers Collection. Long quotations from recent books are shortened here.