In general, especially in the western US as I'm sure you know, it's hard to rely on maps to tell you how drive-able very secondary roads are. They can range from being pretty decent for even just a passenger car and mostly just normal driving skills to you'd better have a Jeep and know how to drive it to "Nah. This isn't really a road." With the weather/season/when was the last flash flood entering into the equation as well.

There are some very sad stories related to people assuming that a road on a map is actually a road in the way people living around cities generally think of the term.