So, the takeaway from your post and that map you created is that you have no actual knowledge of how things are done in the county, other than what you've come across on the internet.
The entire county operates on the 700 MHz ASTRO 25 TDMA system. Fire uses that system for response and operations. Every department has mobiles and portables on the system. The majority of the mobiles are APX 6500, and portables are APX 6000, although there are maybe two dozen or so other models in use by some departments at this point. Nearly all chief officers and apparatus have mobiles installed, and most departments issue portables to their officers, as well as equipping at least some of the apparatus with portables. There are a few exceptions, but not many, including some departments that have multi-band radios such as the APX 7x00 or 8x00.
Fireground/interior ops take place on the UHF "Tact" channels 1-6, with New City FD operating on their own frequency that has been referred to as "Tact 7" in recent years. Although the UHF frequencies are licensed at low power, there are plenty of UHF mobiles in the county.
There are no bidirectional crossband links between UHF and 700, although Fire 1 is repeated over 470.800 via a hardware link the county installed years ago. Paging preempts that link.