Southern Boundary of Idaho
The northern boundary of Utah Territory was set at the 42nd Parallel, which had been the northern edge of Mexico at the time Spain gave up any claims north of this line in the Adams-Onis Treaty of 1819.
The precise location on the ground of this boundary was a contentious issue, as most of the Mormon settlers in southeastern Idaho either believed they were, or wished they were, living in Utah (or Deseret), which was defined to included the drainage basin of the Bear River.
|(image left) Historical map of various borders of the state of Idaho. After Wells (1966). Ironically the arbitrary southern border was never changed
Oscar Sonnenkalb, a German surveyor, who lived in Oxford and Pocatello from 1881 to 1928 and describes life in early Idaho in an elegant little book edited by P.T. Harstad, quotes (1972, p. 2) a letter dated August 15, 1868 from LaFayette Cartee, Surveyor General of Idaho, who
"urged the running of the boundary between the Idaho territory, Utah, and Nevada, at an early day... In the southern part of this country, particularly along the Bear River valley, is an extent of fertile country, and it is estimated that over 3,000 persons are settled here who refuse to pay taxes to this (Idaho) Territory, but pay both taxes and tithes to Utah... The consequence is, this country is, to all intents and purposes, disorganized."
A Government Survey in the early 1870s precisely located the 42nd Parallel and confirmed placement of the Idaho-Utah border. The U.S. Geological Survey places the date of the survey at 1871 (van Zandt, 1966). Sonnenkalb (Harstad, 1972) cites the date as 1872. Though no part of Utah had officially been north of the 42nd Parallel, a Mormon historian, quoted by Sonnenkalb, wrote that with the completion of the boundary survey,
Several times after 1872 the Mormon communities of the Bear River area attempted and failed to become annexed to Utah.
"that part of Utah north of the 42nd Parallel, became a part of Idaho, and the name of Oneida County was given to it."