Ex Smokey was close but not quite;
First here is a blist of how the call signs work:
RadioReference.com - Scanner Frequencies and Radio Frequency Reference Database
Now the number of dispatch channels exceedes the number of RTO's (sorry, PSD {they now like to be called public safety dispatchers over radio telephone operators}) on duty on an almost daily and shift basis. The allocation of the dispatch channels to the RTO's is controlled by a computer. Depending on how busy an individual RTO is the computer may assign additional dispatch channels or take some away. The individual RTO's may drop and pick up dispatch channels as they need/want to also. Say a unit wants to make a crime broadcast to multiple areas, he will simply ask the RTO to pick up those channels also before he begins his broadcast. One of the most popular ones is TSB (transit) a lot of units like them to get their broadcasts because those guys are every where. Also if a unit has emergent traffic the RTO will usually dump all her other channels so she can concentrate on the emergency at hand. You will sometimes hear emergent traffic say from Compton (disp 9) while listening to say Temple (disp 11). Then it will all go quiet, you may hear a new RTO say something like, "Temple your now clear". That lets the Temple units know their freq. is now clear for routine traffic. This could also explain why you heard Norwalk on a busy channel but when you switched over yourself there was nothing.
Now for assignments;
East Los Angeles covers the county area there and the City of Commerce
Lennox covers county areas called; Vermont, Central, and unincorp. Hawthorne as well as the City of Lawndale
Norwalk covers uninc. Whittier as well as the cities of Norwalk, La Mirada, and La Habra Heights
Temple covers uninc. areas of E. Pasadena, N. San Gabriel, S. San Gabriel, El Monte, MAD (Monrovia, Arcadia, Duarte) as well as the cities of Temple City, Rosemead, South El Monte, Duarte, and
Santa Clarita covers a huge area including the entire north/west uninc. area of L.A. County all the way to Gorman as well as the city of Santa Clarita. They also have a boat assigned to Pyramid Lake.
Altadena is a very small area that covers only the uninc. area known as Altadena just north/west of Pasadena.
San Dimas covers uninc. areas of Azusa and Covina, the San Gabriel Mountains and the city of San Dimas
West Hollywood covers that city as well as Universal Studios and they maintain a sub station at Universal City Walk
Malibu is a part of Lost Hills Station although the Malibu units maintain the old 101 call signs.
Lancaster covers another huge chunk of the desert known as N. Los Angeles County as well as the city of Lancaster
Crescenta Valley covers the uninc. areas of Montrose and the west end of the San Gabriel mountains as well as the city of La Canada/Flintridge
Lakewood is almost all contract cities; Lakewood, Paramount, Hawaiian Gardens, Artesia and at one time included the N. End of Long Beach under a rather unique contract that is no more. They are also home to LASD's original air unit "skyknight" which you will still hear patrolling their skies.
Industry covers uninc. Hacienda Heights, Valinda, E. Valinda, as well as the cities of La Puente and
Pico Rivera covers uninc. Whittier and the city of Pico Rivera
Carson covers that city and some smaller county areas they used to have huge uninc. tracts that were mainly taken over by Century and Compton.
Lomita covers the penninsula area where "Marineland" used to be, including all those cities except Palos Verdes Estates which has their own PD.
Avalon is Catalina Island they also maintain a responsibility for San Clemente Island but since the whole thing is a Navy base their is no need to routinely patrol that.
Century station combines the old Firestone and Lynwood Station areas. They have a huge chunk of county area going from Firestone Park to Willowbrook as well as the City of Lynwood.
Lost Hills Has the Calabasas, Agoura, Hidden Hills, and Malibu contracts as well as vast chunks of uninc. lands
Cerritos Station is funded by the city (it's good to be financially stable) and they are the sole responsibility of that station.
Palmdale, see Lancaster change the names of the cities and add a lot of 3 towed sloths
Marina Del Rey patrols Ladera Heights, View Park, Windsor Hills, Marina Del Rey (both land and water) they also maintain a patrol boat for the Santa Monica Bay and beyond
Compton has that city as well as the uninc. areas of Rosewood, East Rancho Dominguez, and Gardena
Walnut also has Diamond Bar and the uninc. area of Rowland Heights