This info is from the Kelty Government Radio Systems book and may be dated, but SCSO numeric identifiers follow the fairly standard format in the North Bay:
[number (agency)][letter (function)][number (zone/beat)]
The agency number for Sonoma County Sheriff is 10, but I believe it's usually omitted.
Some common function letters are:
A - Administration
C - Civil
D - Detective/Coroner
E - Patrol (Day Watch)
F - Patrol (Eve Watch)
G - Patrol (Mid Watch)
H - Helicopter (10-Henry-1, usually just "Henry 1")
I - Crime Tech
J - Jail
K - Resident Deputy
L - Lake Sonoma Patrol Boat
M - Park Maintenance
O - Helo Support/Rescue
P - Park Ranger
R - Reserve Deputy
S - Sergeant
T - Transportation
U - Community Services
V - Vice
X - Park Aides
Z - Tactical/Narcotics/SWAT
Kelty has Sonoma County Sheriff beats listed as:
10 - Russian River
20 - North
30 - Central & East
40 - West
50 - South
60 - Valley of the Moon
70 - West & Central
80 - Windsor (contract?)
(Sonoma contract is left blank)
It's pretty clear that the first number is the zone number (which correlates with the current zone map), and the second number is probably a beat within that zone. Since there are only six zones on the map, this list may be outdated, or 70 units may serve some other purpose.
Looking at the zone map, I wonder if "Sheriff 3" covers ALL of zones 1 and 6 when it's online, or just the areas around the Russian River and town of Sonoma? I am guessing all of those zones, but I hadn't previously considered it covering the coast all the way up to the northern county line.