20 mi. NE of Jack smith Bay and 38 mi. N of Goodnews, Kilbuck-Kuskokwim Mts.
Originally named "Helmick Mountain" by J. E. Spurr and W. S. Post (in Spurr, 1900, map 10), U.S. Geological Survey (USGS), for Reverend Benjamin Helmick, Moravian missionary who work in this area. The descriptive name "Thumb Mountain" was published in 1915 by U.S. Coast and Geodetic Survey (USC&GS) on Chart 9103. It was so called because "from off Quinhagak it resembles a huge thumb placed on a high flat mountain plateau." (U.S. Coast and Geodetic Survey, 1916, p. 249).
Chingekigtlik Mountain, Ingluilngok Mountain, Island Butte, Island Mountain, Kisogle Mountain, Thumb Mountain,
Rivers:East Fork Arolik River, South Fork Arolik River,
Streams:Bear Creek, Casino Creek, Colorado Creek, Crater Creek, Decemebr Creek, Deer Creek, Flat Creek, Garnet Creek, Keno Creek, Midas Creek, Quickumguila Creek, Tyone Creek,
Valleys: