What you are saying does make sense intuitively, but the facts - as far as my research has taken me - don't support the idea of slaves running West. Looking at the 1870 and 1880 censuses for Nevada, the African American population derives almost exclusively from the Mid Atlantic and Northern states, Massachusetts, Virginia, Kentucky, and Maryland being some of the more common places of origin.

I suppose what may have inhibited runaways from going West was the expanse the region represented. One can easily starve or die of thirst walking West - even with preparation. And there was always the concern in the Antebellum and Civil War periods of being killed by Native Americans. Even if that was not likely to happen, the fear of native violence was widespread.

In short, with little by way of provisions and less by way of knowledge about how to survive the expanse of the arid West, I probably would have run north if given a chance.