n4voxgill and Mick provided some very good information. For those who do not know the southern California area here are a few more facts. There are about 90 incorporated cities in Los Angeles County alone. Many of these cities obtain their police and fire protection by contracting with L.A. County. Almost all of the cities are intermingled with each other and with small islands of unincorporated, but densely urban, areas where the county is responsible for all services. The southern California metro area consists of five counties, Los Angeles, Orange, Riverside, and San Bernardino. The contiguous urban area of southern California is connected to all or portions of these five counties. These counties also have intermingled incorporated and unincorporated areas laid out in a very complex manner.
The area also has a complex system of special districts for water, sewer, and other services including the Metropolitan Water District, which delivers a massive amount of water from the Colorado River. The state Department of Water Resources and the LA City Department of Water and Power have a massive infrastructure to deliver water. The system of aqueducts, reservoirs, and power lines is the largest in the nation. The area has one of the busiest harbors in the world and an extremely busy airport, along with four busy regional airports. At one time it was estimated that of all the aircraft in the country flying at any one time, that 1/4 of it was over the L.A. Metropolitan area.
The area includes lands in National Parks, National Forests, Bureau of Land Management public lands, Indian reservations, Army Corps of Engineers operated dams, Military bases, and State Parks. As a group the four National Forests of southern California are the most heavily used in the National Forest System and their management complexity is enormous. The Calif. Department of Forestry and Fire Protection provides fire protection for state responsibility areas and provides local fire services to some local jurisdictions by contract. Other federal agencies with a highly visible presence in the area include the Border Patrol, FBI (it is the bank robbery capital of the U.S.), Coast Guard, FAA, Customs, DEA, State Dept., and ATF.
The California Highway Patrol and Caltrans (Calif. Dept of Transportation) patrol and maintain the freeways and a long list of major highways. The traffic volumes on these roads is the highest in the nation.
The area is home to a large system of railroads and railroad operations such as locomotive maintenance, track maintenance, and car repair. Local rail transportation is becoming more important all the time with several major routes and a growing subway system.
The area is home to oil refineries, major manufacturing, chemical plants, and nuclear power plants.
The wildland/urban interface is the most complex in the world. Wildland vegetation is of the type that grows quickly and burns with incredible intensity and speed. Due in part to fire, the area has some of the worst mudslides in the nation. The area is subject to relatively frequent earthquakes, although a major earthquake had not occurred in several hundred years. A scenario for a major earthquake would be an 8.0 on the San Andreas fault near the intersection of Interstates 10 and 15 and event that would cause enough injuries to fill every hospital bed in the western world. The area is not subject to frequent tornadoes, flooding is not of the type the Midwest and east experience, although the flooding after watersheds above the urban areas following a big fire season is quite destructive. The center of hurricanes do not cross over the area. Snow is rare over much of the urban portions of the area, but falls with regularity over the mountains that ring the urban area, and can sometimes be sufficient in depth over the high deserts to cause major problems. Wind is a problem, not only for wildland fire, but in how destructive it can be in urban areas. The area has a heavy search and rescue workload due to the rugged terrain of the mountains, the heat of the deserts, and the Pacific Ocean.
I've probably left out some ingredients in my list which show how complex this area is and the need for interoperability. If interoperability can be achieved here, it is likely that it can be provided anywhere. It is a great place to listen to a scanner, with major action occurring very frequently. The complexity of the area with its tendency for major incidents lead to the development of the incident command system. Many agencies such as fire departments and police departments are among the best in the world. Like the article said they work together all the time, but have trouble talking with each other.