SR 89 begins at an intersection with US 395. The highway goes west through a few switchbacks before crossing into Alpine County and the Humboldt-Toiyabe National Forest.[5] The route over Monitor Pass is typically closed during the winter due to snow accumulation.[6] SR 89 continues by Heenan Lake before intersecting with the eastern end of SR 4 and turning northwest, passing through Markleeville. SR 89 continues northwest to the town of Woodfords, where it turns west, running concurrently with SR 88 for a brief distance before turning into El Dorado County.[5] The section of SR 89 from SR 88 north to US 50 is co-signed as US 50 Alternate for use as a detour for when US 50 closes.[citation needed]
SR 89 runs concurrently with I-80 eastbound briefly before exiting to the north and continuing through Truckee and passing near Prosser Creek Reservoir outside of the town limits. SR 89 continues through Hobart Mills before crossing into Sierra County and continuing northwest to Randolph and Sierraville, where it shares a wrong-way concurrency with SR 49 through the town of Sattley; they then intersect CR A23 before SR 89 splits off to the northwest. SR 89 continues through Calpine before crossing into Plumas County.[5]
SR 36 and SR 89 intersect the northern terminus of SR 32 and SR 172 before SR 36 splits off to the west and SR 89 enters Lassen Volcanic National Park.[5] The SR 89 state designation officially does not run through the national park, and this segment is directly under the park's jurisdiction instead of Caltrans. When it is open, a park fee is charged. The segment through the park is typically closed during the winter due to very heavy snowfall and snowpack.[8] Outside the other park entrance in the northwest corner in Shasta County, SR 89 forms a concurrency with SR 44, heading northeast to Old Station.[5]
One point of interest along California State Route 89 includes the Pony Express remount station in Woodfords, the Lake Tahoe Outlet Gates in Tahoe City (control of these gates was the source of the two-decade "Tahoe Water War" between lakeshore owners and downstream Truckee River water users), Plumas-Eureka State Park (containing Johnsville, a well-preserved '49er town, and Pioneer Ski Area, the first sport skiing area in the Western hemisphere), Lake Almanor and Lassen Volcanic National Park.
Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage. R reflects a realignment in the route since then, M indicates a second realignment, L refers to an overlap due to a correction or change, and T indicates postmiles classified as temporary (for a full list of prefixes, see California postmile § Official postmile definitions).[17] Segments that remain unconstructed or have been relinquished to local control may be omitted. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.
^"Article 2 of Chapter 2 of Division 1". California Streets and Highways Code. Sacramento: California Office of Legislative Counsel. Retrieved February 6, 2019.
^Federal Highway Administration (March 25, 2015). National Highway System: California (North)(PDF) (Map). Scale not given. Washington, DC: Federal Highway Administration. Retrieved October 8, 2017.
^Natzke, Stefan; Neathery, Mike & Adderly, Kevin (June 20, 2012). "What is the National Highway System?". National Highway System. Washington, DC: Federal Highway Administration. Retrieved July 1, 2012.
^California Department of Transportation (2012). Scenic Highway Guidelines(PDF). Sacramento: California Department of Transportation. p. 5. Retrieved June 8, 2017.
^ abCalifornia Department of Transportation. "State Truck Route List". Sacramento: California Department of Transportation. Archived from the original(XLS file) on September 5, 2015. Retrieved June 30, 2015.