Starting in Roosevelt at the intersection with US-40/US-191 (200 East), the route travels west for approximately one half mile, before turning northwest, then turning north through Cedarview to Neola. In Neola, the route makes a right turn onto 9000 North and begins travelling east. It generally follows this easterly direction across the Duchesne County/Uintah County county line, through Lapoint, before entering Vernal. In Vernal, the route makes a right turn, and travels south for less than one mile (1.6 km) before terminating at the intersection with Main Street US-40/US-191 (Main Street).
History
The state legislature added the entire length of SR-121 to the state highway system in 1931 (though it was known as SR-122 until 1933).[2][3] The route was truncated in 1953 to run only from Roosevelt to the east of Lapoint.[4] A short piece at the east end was redesignated State Route 245, from Vernal west to the bridge over the Highline Canal west of Maeser, but the more rugged section between the bridges was removed from the state highway system.[5] This split was undone in 1969, when SR-121 again became a continuous route from Roosevelt to Vernal.[6]
^Utah State Legislature (1931). "Chapter 55: Designation of State Roads". Session Laws of Utah. (122) From Vernal westerly via LaPoint to Neola, to Roosevelt.
^Utah State Legislature (1933). "Chapter 30". Session Laws of Utah. (121) From Vernal westerly via LaPoint to Neola, thence southerly to Roosevelt.
^Utah State Legislature (1953). "Chapter 45: Designation of State Roads". Session Laws of Utah. Route 121. From Roosevelt on route 6 northerly to Neola, thence easterly via Lapoint to and across Gerber Ditch Bridge.
^Utah State Legislature (1953). "Chapter 45: Designation of State Roads". Session Laws of Utah. Route 245. From Vernal on route 6 westerly via Maeser to and across High Line Canal bridge.
