The segments from Pierre to US 212 and from Mobridge to the North Dakota state line are parts of the Lewis and Clark Trail.

The southern segment of SD 1804 begins on the eastern shore of the Missouri River, a few miles south of Geddes.

It curves to the northeast and travels through the southern part of that area, crossing over Platte Creek in the process.

SD 1804 then passes the Spring Creek Recreation Area and enters Sully County.

It curves back to the east for a short distance before encountering an intersection with 293rd Avenue and Agar Road.

SD 1804 continues to the north and crosses over Artichoke Creek and then intersects US 212 just southeast of Forest City.

It passes the Thomas Bay Recreation Area and proceeds to an intersection with 130th Street, which leads to Glenham.

Here, SD 1804 turns left and proceeds in a due-west direction on 130th Street, while 294th Avenue continues straight ahead.

The three highways travel concurrently to the west and enter Mobridge, where SD 1804 splits off onto 4th Avenue East.

It travels to the north, passing Legion Memorial Park, and then leaves the city limits of Mobridge.

It then passes Mobridge Municipal Airport, Greenwood Cemetery, and Oahe Hills Country Club.

A short distance later, it turns to the left and resumes its northward direction, while 126th street continues straight ahead.

At an intersection with the southern terminus of 299th Avenue, SD 1804 turns left onto 102nd Street and travels to the west-northwest.

The highway curves to the north-northwest and reaches its northern terminus, an intersection with 102nd Street at the North Dakota state line.