I believe their old transmitter was in El Monte.
Yes you're right and we all know the L.A. County Fair isn't in Ontario but Pomona as well. This information can be easily found in the FCC database or Wikipedia:
In 1987 KRLA moved its transmitter site from South El Monte to Irwindale, where a similar antenna array was installed.[23] During the 1990s, KRLA was authorized to increase nighttime power from 10,000 to 20,000 watts. When the power increase went into effect, KRLA started broadcasting from the new transmitter site in Irwindale. This is a few miles north of the old El Monte site.[23]
The El Monte transmitter building still stands as a shell. The entire inside is burned out; however, there are still clues to its historic past, namely the first incarnation of its directional antenna arrays (four in-line 135-degree towers, one days, four nights), the second incarnation (four 135-degree towers in a parallelogram, days and a 90-, two 135-, and a 180-degree towers, nights), and the last incarnation, with seven total towers, four days and four nights, with one tower in common, days and nights). There are numerous ducts to keep the equipment cool and an underground channel to divert the cooling water for the transmitters. A well nearby supplied the water. Still visible is the wooden archway where the transmission cables gently bent toward underground conduits running to the transmission towers in the nearby field. All that remains of these towers are the concrete pylons, all aligned as described.[citation needed]
The present Irwindale site includes five 135-degree towers, two days and four nights, with one in common. The significantly northern location, relative to the old El Monte site, allows the large "Inland Empire" to be served with 50,000 watts and only two towers, not four, days, and the greater Los Angeles metro to be served with 20,000 watts and four towers, nights.