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According to the Washington State Department of Fish and Wildlife, the boat ramp named Southwest Bonaparte Lake Road is located on the southwest shore of Bonaparte Lake, near the town of Tonasket. This boat ramp is open to the public and provides access to the lake for various types of watercraft, including motorboats, rowboats, canoes, and kayaks.

The boat ramp is described as a "primitive" facility, meaning that it does not have any amenities such as restrooms or parking areas. However, it is maintained by the state and is accessible to most types of vehicles, including trailers.

In terms of width, the boat ramp appears to be narrow, with room for only one vehicle and boat at a time. However, it is noted that the lake is relatively small and does not receive heavy boating traffic, so the narrowness of the ramp is not likely to be a significant issue.

Based on the available information, it appears that the Southwest Bonaparte Lake Road boat ramp is a basic facility that provides access to a small lake in north-central Washington. While it may not be the most luxurious boat ramp in the state, it serves its purpose by allowing visitors to enjoy the natural beauty of Bonaparte Lake and its surroundings.