Title: Geography of South Dakota
Content:  to separate South Dakota from Montana and Wyoming during the transition to statehood. The northern border is the 46th parallel north and was originally marked by 720 quartzite monuments over 360 miles of prairie. Two time zones cover South Dakota; the state is split roughly in half between the Central Time Zone (UTC-6) in the east and the Mountain Time Zone (UTC-7) in the west. The boundary between the two zones runs south down the Missouri River until Pierre, at which point the boundary roughly continues due south while the river turns southeast. The North American continental pole of inaccessibility is in Bennett County, located 1024 mi (1650 km) from the nearest coastline, between Allen and Kyle (Oglala Lakota County) at 43.36°N, -101.97°W.
Title: Time in South Dakota
Content:  South Dakota lies in both the Mountain Time Zone and the Central Time Zone. Mountain Time roughly contains the western half of the state, but not all of it. Rapid City is the largest city in the Mountain Time portion of the state. Central Time contains the eastern half of the state and roughly more of the state than the Mountain Time Zone and includes the state capital Pierre and the largest city, Sioux Falls.
Title: Time in North Dakota
Content: Bowman County ; Adams County ; Slope County ; Hettinger County ; Grant County ; Stark County ; Billings County ; Golden Valley County ; Parts of Sioux County, Dunn County, and McKenzie County About 75% of North Dakota is in the Central Time Zone, while the southwest quarter is in the Mountain Time Zone. Mountain Time is observed in: Central Time is observed throughout the rest of the state.
Title: Time in the United States
Content: divides the southwest portion of North Dakota from the rest of the state ; divides South Dakota roughly in half ; divides the western third of Nebraska from the rest of the state ; divides a very small portion of extreme western Kansas bordering Colorado (Greeley, Hamilton, Sherman, and Wallace counties) from the rest of the state (three other counties which border Colorado—Cheyenne, Morton, and Stanton counties—observe central time) ; follows the border between New Mexico (west) and Oklahoma (east) (although the zone legally begins at the Oklahoma–New Mexico state line, Kenton in extreme northwestern Cimarron County, Oklahoma unofficially observes mountain time) ; follows the border between New Mexico (west) and Texas (east) ; divides El Paso County, Hudspeth County, and a portion of northwestern Culberson County that includes eastern Guadalupe Mountains National Park from the rest of Texas 
Title: Time in South Dakota
Content:  The 2 zones for South Dakota as given by zone.tab of the IANA time zone database. Columns marked * are from the zone.tab.
Title: Time in the United States
Content:  42nd parallel north to longitude 114.041726 W. ; turns south and follows the border between Nevada (west) and Utah (east), except for following the west city limit line of West Wendover dividing it from the rest of Nevada, and putting it in the mountain time zone. Jackpot, Nevada, just south of the 42nd parallel and some 25 mi west of the time zone south turn, also observes mountain time, on an unofficial basis. ; follows the border between Nevada (west) and Arizona (east) ; follows the border between California (west) and Arizona (east), mostly defined by the Colorado River, to the border between the U.S. and Mexico. 
Title: Todd County, South Dakota
Content:  Todd County lies on the south line of South Dakota. Its south boundary line abuts the north boundary line of the state of Nebraska. Its terrain consists of semi-arid rolling hills, cut by gullies and drainages which flow to the northeast. The land is partially dedicated to agriculture, including center pivot irrigation. The terrain slopes to the northeast, and its highest point is near the SW corner, at 3,176' (968m) ASL. The eastern portion of South Dakota's counties (48 of 66) observe Central Time; the western counties (18 of 66) observe Mountain Time. Todd County is the westernmost of the SD counties to observe Central Time. Todd County has a total area of 1391 sqmi, of which 1389 sqmi is land and 2.3 sqmi (0.2%) is water.
Title: Time in the United States
Content: follows the border between northern Idaho (to the west) and northwestern Montana (to the east) ; turns west at 45.55767°N, -114.56483°W (just south of Nez Perce Pass), and follows the Idaho County line to the Salmon River ; follows the Salmon River west to the town of Riggins, where the Salmon River turns north. This puts almost all of northern Idaho in the Pacific time zone, except for the small loop described next. ; turns north and follows the Salmon River to the Snake River at the Oregon border (at 45.855°N, -116.79167°W). This loop to the north creates a curious situation where one can enter a more westerly 
Title: Frank R. Gooding
Content:  In the 1920s, the Interstate Commerce Commission (ICC) had the western two-thirds of Idaho in the Pacific Time Zone. Gooding sponsored a bill in the Senate to place all of southern Idaho in the Mountain Time Zone, which stands today. The dividing line is the Salmon River at about 45.5° N, approximately midway from the borders with Nevada (42° N) and British Columbia, Canada (49° N).
Title: Geography of South Dakota
Content:  South Dakota can generally be divided into three regions: eastern South Dakota, western South Dakota, and the Black Hills. The Missouri River serves as a somewhat stark boundary in terms of geographic, social and political differences between eastern and western South Dakota, and the geography of the Black Hills differs from its surroundings to such an extent that it can be considered separate from the rest of western South Dakota. South Dakotans also at times combine the Black Hills with the rest of western South Dakota, and refer to the two resulting regions, divided by the Missouri, as West River and East River. Eastern South Dakota is generally wetter and features lower topography than the western part of the state. Smaller geographic regions of 

Question: where is the time zone line in south dakota?
Answer: Mountain Time Zone.