Question: Deer Medicine Rocks is a sandstone formation located in what county in Montana?

Context paragraphs:
Upper Karroo Sandstone Formation: The Upper Karroo Sandstone Formation is a geological formation dating to roughly between 200 and 175 million years ago and covering part of the Early Jurassic.  The Upper Karroo Sandstone Formation is found in Zimbabwe and is a member of the Karoo Supergroup.  As its name suggests, it consists partly of sandstone.  Fossils of the prosauropod dinosaur "Massospondylus" have been recovered from the Upper Karroo Sandstone.

Medicine Rocks State Park: Medicine Rocks State Park is a park owned by the state of Montana in the United States.  It is located about 25 mi west-southwest of Baker, Montana, and 11 mi north of Ekalaka, Montana.  The park is named for the "Medicine Rocks," a series of sandstone pillars similar to hoodoos some 60 to high with eerie undulations, holes, and tunnels in them.  The rocks contain numerous examples of Native American rock art, and are considered a sacred holy place by Plains Indians.  The park is 330 acre in size and 3379 ft in elevation.  It is managed by the Montana Department of Fish, Wildlife and Parks.  Theodore Roosevelt said Medicine Rocks was "as fantastically beautiful a place as I have ever seen".  The park was listed on the National Register of Historic Places in 2017.

Bushveld Sandstone Formation: The Bushveld Sandstone Formation is a geological formation dating to roughly between 228 and 223 million years ago and covering the Carnian to Norian stages.  The Bushveld Sandstone Formation is found in South Africa and is a member of the Stormberg Group.  As its name suggests, it consists mainly of sandstone.  Fossils of the prosauropod dinosaur "Massospondylus" have been recovered from the Bushveld Sandstone.

Aylesbeare Mudstone Group: The Aylesbeare Mudstone Group is an early Triassic lithostratigraphic group (a sequence of rock strata) in southwest England.  The name is derived from the village of Aylesbeare in east Devon.  The Group comprises the Littleham Mudstone Formation, the Exmouth Mudstone and Sandstone Formation and the underlying Clyst St Lawrence Formation.  The strata are exposed on the coast between Exmouth and Budleigh Salterton where the type section is defined.  The rocks of the Aylesbeare Mudstone Group have also previously been known as the Aylesbeare Group and the Aylesbeare Mudstone Formation.

Otter Sandstone Formation: The Otter Sandstone Formation is an obselete geological unit in England, now referred to as the Helsby Sandstone Formation.  It preserves fossils dated to the Triassic, Anisian period.

Deer Medicine Rocks: Deer Medicine Rocks (Siouan: Baáhpashxxaawe, literal translation "Antler Rocks") is a sandstone formation located on the west bank of Rosebud Creek in the vicinity of Lame Deer, Montana, United States.  The formation is significant for its association with the Great Sioux War of 1876-77, and its connection with Sitting Bull's visionary sun dance of early June 1876 which prophesied victory at the Battle of the Little Bighorn.  At its nomination to National Historic Landmark status in 2011, it was described as the only site to offer "a wholly Native American historical interpretation of the Battle of the Little Big Horn."

Langeronyx: Langeronyx is an extinct genus of basal rhynchosaurid known from the early Middle Triassic (Anisian stage) Bromsgrove Sandstone Formation of Warwickshire, UK.  It contains a single species, Langeronyx brodiei, originally included in the genus "Rhynchosaurus".  "R. brodiei" was first described and named by Michael Benton in 1990, but its redescription by Martín D. Ezcurra, Felipe Montefeltro and Richard J. Butler in 2016 recovered it as more closely related to the more advance hyperodapedontine than to the type species of "Rhynchosaurus" and thus it was moved to its own genus.  The generic name "Langeronyx" honors the Brazilian paleontologist Max Cardoso Langer in recognition of his rhynchosaur research, combined with the Greek "onyx" ("óνυξ") meaning "claw", a common suffix for rhynchosaur genera.  "L. brodiei" is known solely from the holotype, a partial skull divided into the two specimens WARMS G6097/1 and NHMUK PV R8495, housed in the Warwickshire Museum, Warwick and Natural History Museum, London, respectively.  Other specimens originally referred to "R. brodiei" either do not overlap with its type or can be just as likely referred to other basal rhynchosaurids (like "Fodonyx spenceri" and "Bentonyx sidensis" from the coeval Otter Sandstone Formation, UK).  "L. brodiei" is one of two basal archosauromorphs known from the Bromsgrove Sandstone Formation, the other being the lesser known "Rhombopholis scutulata".

Sinbad Formation: The Sinbad Formation is a geologic formation in Utah initially named and described by James Gilluly and J.B. Reeside Junior in the 1920s.  It is known for preserving fossils dating back to the Early Triassic Period.  The Sinbad Limestone Member is a portion of the greater Moenkopi formation, and is made up of beds of yellowish-gray limestone, dolomite, quartz sandstone, siltstone and, conglomerate rock.  These beds range in thickness from 10 to 103 feet and hold fossils of Meekoceras fauna from the lower Triassic stage of history.  The area was once covered in shallow seawater that deposited sediment and marine life that would later comprise the sandstone formation.

Las Juntas Formation: The Las Juntas Formation or Las Juntas Sandstone (Spanish: "(Formación) Areniscas de Las Juntas" , Kiaj, Kialj, K1j) is a geological formation of the Altiplano Cundiboyacense and Tenza Valley, Eastern Ranges of the Colombian Andes.  The Las Juntas Formation is found in the departments Cundinamarca, Boyacá and Casanare.  The predominantly sandstone formation dates to the Early Cretaceous period; Hauterivian epoch, and has a maximum thickness of 910 m .

Lame Deer, Montana: Lame Deer (Meaveʼhoʼeno in Cheyenne) is a census-designated place (CDP) in Rosebud County, Montana.  The community is named after Miniconjou Lakota chief Lame Deer, who was killed by the U.S. Army in 1877 under a flag of truce south of the town.  It is the tribal and government agency headquarters of the Northern Cheyenne Indian Reservation.  This is the location of the Chief Dull Knife College and the annual Northern Cheyenne Powwow.

Supporting paragraphs: Deer Medicine Rocks Lame Deer, Montana
Answer: Rosebud County