Encouraged by a faulty assay report, the Morning Star claimholders built a smelter in 1886 to test for silver, but the test showed only zinc, and the smelter remained standing as a symbol of the early mining period. From the 1880s to the 1920s, Rush boomed as the hills and hollows yielded zinc ore, and the discovery of zinc there encouraged mining development throughout northern Arkansas and brought jobs and prosperity across the region. The first ore discovery at Rush was made at the Morning Star Mine, named by claimholder Jim McCabe for the moon's early morning position over the mine, and the Morning Star became Rush's most famous mine and nationally respected. A small community grew up around it, with residences, stores, a hotel, a livery barn, and a doctor's office intermingled with the mining facilities, and the name Rush became synonymous with the entire mining area. The Morning Star Mining Company held its land until the 1960s, when the property was sold and many of the remaining buildings were removed. In the Rush district, rocks date from the Early Ordovician to Mississippian, with the ore zone in the limestone and dolomite of the Everton formation, and faulting and erosion exposed the mineralized zones, allowing horizontal tunnel access instead of shafts.