Question: When was the Montana city with the population of 4,223 named?

Context paragraphs:
Mineral County, Montana: Mineral County is a county located in the U.S. state of Montana.  As of the 2010 census, the population was 4,223.  Its county seat is Superior.

KHGC: KHGC (98.5 FM) is a radio station broadcasting a Christian format.  Licensed to Montana City, Montana, the station is owned by Hi-Line Radio Fellowship, Inc., and broadcasts its network Your Network of Praise.

KWLG-LP: KWLG-LP (105.9 FM) is a radio station broadcasting a variety format.  Licensed to Montana City, Montana, United States, the station serves the Helena, Montana, area.  The station is currently owned by Jefferson County Disaster & Emergency Services.

Confederate Gulch and Diamond City: Confederate Gulch is a steeply incised valley on the west facing slopes of the Big Belt Mountains in the U.S. state of Montana.  Its small stream drains westward into Canyon Ferry Lake, on the upper Missouri River Valley near present-day Townsend, Montana.  In 1864 Confederate soldiers on parole from the American Civil War made a minor gold discovery in the gulch, but in 1865 the discovery of the sensationally rich Montana Bar—one of the richest placer strikes per acre ever made—led to other rich gold strikes up and down the gulch, and touched off a frantic boom period of placer gold mining that extended through 1869.  From 1866 to 1869 the gulch equaled or outstripped all other Montana Territory mining camps in gold production, producing an estimated $19 to $30 million in gold—late 1860s money.  For a time, the gulch became the largest community in Montana—in 1866 Montana had a total population of 28,000, and of these, about 10,000 (35%) were working in Confederate Gulch.  The main community was Diamond City , and while gold production was at its height, Diamond City roared along both night and day.  During its heyday, Diamond City was the county seat of Montana's Meagher County, although today the area has become part of Broadwater County.  In their frantic efforts to get at more gold, the miners built ditches and flumes that extended for miles, and employed high pressure hydraulic mining methods which washed down whole hillsides and ate up the gulch floor.  The hydraulic mining process stripped the gulch and left huge spoil banks—hydraulic mining even consumed the site of Diamond City, which had to be moved to a new location.  Then the gold ran out, the boom was over and the population simply picked up and left.  In 1870 there were only 255 people left and a year later only about 60.  Today hardly a trace remains of Diamond City or the other gulch communities.  The gulch is quiet and empty, with only an occasional summer prospector, or a rare traveler using the unimproved road that still winds up the gulch from the Missouri Valley and crosses the top of the Big Belts on its way down to the Smith River Valley.  Diamond City, Confederate Gulch and the Montana Bar were spectacular examples of the flash-in-the pan Montana placer gold mining camps, but what a flash.

Kirk Wagoner: Kirk Wagoner is an American politician.  He serves as a Republican member of the Montana House of Representatives, where he represents District 75, including Montana City, Montana.

Elkhorn Mountains: The Elkhorn Mountains are a mountain range in southwestern Montana, part of the Rocky Mountains and are roughly 300,000 acres (1200 km²) in size.  It is an inactive volcanic mountain range with the highest point being Crow Peak at 9414 ft , right next to Elkhorn Peak, 9381 ft .  The range is surrounded by the cities of Helena, Montana City, Townsend, Whitehall, and Boulder and is part of the Helena National Forest in Montana's Jefferson County.

Montana City, Montana: Montana City is a census-designated place (CDP) in Jefferson County, Montana, United States.  The population was 2,715 at the 2010 census.  It is part of the Helena Micropolitan Statistical Area.

Montana City, Colorado: Montana City was the first settlement in what was later to become Denver, Colorado.  It was established during the Pikes Peak Gold Rush on the east bank of the South Platte River, just north of the confluence with Little Dry Creek, in 1858.  At the time, the site was in the Kansas Territory.

Superior, Montana: Superior is a town in and the county seat of Mineral County, Montana, United States.  The population was 812 at the 2010 census.  Superior was named after its founders' hometown of Superior, Wisconsin in 1869.  The post office was established in 1871 after Mineral County became the site of one of the largest gold strikes that helped settle the West.

Grant-Frontier Park: Grant-Frontier Park is a park at Evans Ave. on the east bank of the South Platte River in southwest Denver, Colorado.  It is the site of the Montana City settlement.  The park was named in honor of Grant Junior High School (now Grant Middle School) whose teachers and students were responsible for discovering the site, cleaning and restoring it, and researching the history of Montana City.

Supporting paragraphs: Superior, Montana Mineral County, Montana
Answer: 1869