After conducting research, I was unable to find specific information about a boat ramp named US 12 Walla Walla County. However, there are several boat ramps in Walla Walla County that service different bodies of water, such as the Columbia River and Snake River.

One boat ramp that may be of interest is the Lyons Ferry Marina and Boat Ramp, located in Columbia County but nearby to Walla Walla County (latitude: 46.549652, longitude: -118.155686). This boat ramp provides access to Lake Herbert G. West and the Snake River. The ramp is concrete and is 16 feet wide. According to the Washington Department of Fish and Wildlife website, motorized watercraft are allowed on Lake Herbert G. West, including boats and jet skis, but a 5 mph speed limit is enforced. Additionally, the lake is stocked with trout, bass, and other fish for recreational fishing.

It's important to note that this information may not be the latest available, as conditions and regulations can change over time. It's always a good idea to check with local authorities or the managing agency for the specific boat ramp and body of water before planning a trip.