Glendale Model Railroad Club
Operators of the Verdugo Valley Lines, a large HO scale layout in Glendale

Los Angeles Live Steamers Railroad Museum
Operators of a large outdoor 7-1/2" gauge railroad in Griffith Park

Southern California Live Steamers
Operators of an outdoor 7-1/2" gauge miniature railroad in Wilson Park, Torrance

Los Angeles N Scale Association
Operators of the East Valley Lines, a large N scale layout at Travel Town in Griffith Park

Highland Park Society of Model Railroad Engineers
Operators of the Highland Pacific Railroad, a large HO layout in San Gabriel

Los Angeles Model Railroad Society
Operators of the Great Lakes & Western, a large HO scale layout in Hawthorne

Pasadena Model Railroad Club
Operators of the Sierra Pacific Lines, a very large HO scale layout in east Los Angeles

Santa Susana Railroad Historical Society
Operators of the Santa Susana Pacific, a large HO scale layout in Simi Valley

Slim Gauge Guild
Operators of two large narrow gauge layouts in Sn3 and HOn3, in Pasadena

'20s & '30s Modular Model Railroad Club
Operators of beautiful HO scale modules set in time between 1920 and 1939

California Southern Model Railroad Club
Operators of a large "mushroom double deck" HO scale layout in Norwalk

Belmont Shore Model Railroad Club
Operators of a large N scale layout in San Pedro, and originators of N-Trak

Angels Gate Hi-Railers Model Railroad Club
Operators of a large O-Gauge Hi-Rail layout in San Pedro

Amtrak Employees Model Railroad Club
Operators of a 2-story HO scale layout in the Amtrak engine facility in Los Angeles

Antelope Valley Model Railroad Club
Operators of an HO scale layout in a Pullman passenger car in Lancaster

Fairplex Garden Railroad
Operators of an outdoor G gauge layout in the L.A. County Fairgrounds in Pomona

Southern California Traction Club
Operators of a modular HO scale traction layout, with a clubhouse in Baldwin Hills

Gold Coast Modular Railroad Club
Operators of HO scale modules, with a setup in the Murphy Auto Museum, Oxnard

Antelope Valley N' Scalers
Operators of NTRAK modules, no fixed layout, based in the Antelope Valley

Group 160 NTrak Club
Operators of N scale modules, no fixed layout, based in Burbank

Pomona Valley Model Railroad Club
Operators of the Sierra, Cajon & Pacific HO scale layout, seeking a new facility, now meeting at members' homes

Inland Terminal Model Railroad Club
Operators of an S scale layout in Lawndale, no website, at 4734 W. 152nd Street, Wednesday evenings.

Currently on hiatus:
Citrus Empire Model Railroad Club
The O scale club was formerly located in the Los Angeles County Fairgrounds at Pomona. Their modular group is still active. They have use of a member's home layout in a garage building in West Covina.

Apparently defunct in 2008:
Foothill Model Railroad Club
The HO scale club had a layout in Glendale, and put on the popular Sunland swap meets.