Hey all, I know it says I'm in Maryland, but I lived in Cali for a few years.
198 is in central cali, just east south east of Monterey(where I lived).
You can get directly on it from US Rt. 101 which I would recommend. It'll take you along a very twist, very deserted canyon road with a place in the middle called Preist Valley Station, which is a restaurant/bar which you can smoke in(apparently, the only in cali cuz cali don't know it's there).
Conituing on, 198 will take you by LeMoore NAS and on to Vasalia and Lemoncove. After that it pretty much ends.
The stretch of 198 from 101 has newly been resurfaced however caution should be taken as the rumble reflectors have been installed on the yellow lines which all the cali folks know can really upset cornering traction.
There are no other routes out of there other than Rt. 99 which is near LeMoore. So when going in, remember you have to drive back out.