I'm not from the area but I travel through there often and try to keep tabs on what's new anywhere I go but here is a brief view of the most active that I have in my base in my pickup. All are monitored on the output freqs.
155.595 is Box Elder PD Dispatch (County SO, Brigham, Tremonton et al)
154.665 is a repeater for the north part of the county of the above (can be heard clear in Cache)
154.355 is Box Elder Fire Dispatch
154.145 is Box Elder Fire 2
154.430 is Brigham City EMS
154.740 is Brigham City PD Car To Car (C2C)
155.520 is Tremonton C2C
I have some that are licensed for Mantua, Honeyville, Garland and Perry but those areas (at least those with PD's) I hear their C2C traffic on the UHP Ch 3 (155.745) which in the rural parts of the state is used by both UHP and local sheriffs.
As far as 800, the site at Promontory has coverage to the Idaho state line and rumor has it that a new 800 site will be installed at Hansel Mountain to cover 1-84 to the Idaho state line at Snowville.
That pretty much covers the basics. If anyone has more that are active, holler!
Cheers