An academic study of the quest by explorers and later entrepreneurs to find a way over California's mountain wall. Geographer Howard discusses a critical development in the history of California, the building of the first roads across the Sierra Nevada, tall and snow-blocked mountains that, even at their easier passes, still required days and even weeks to traverse. (The Truckee Pass, where the Donner party met its doom and where Interstate 80 now cuts through the Sierra, was especially difficult, and as Howard notes, ""the paralyzing effect of heavy snowfall remains a threat to trans-Sierra transportation even today."") After surveying the geography of montane California, Howard looks into the careers of the 19th-century explorers who first established various routes over the Sierra, notably Jedediah Smith, Joseph Walker, and John Charles Fremont, and at the rush to build true roads after the US government opened competitive bidding for mail delivery (Wells Fargo eventually won) and Congress passed the Wagon Road Act of 1857, a precursor of the modern federal highway system. Howard offers many interesting asides, some of them buried in endnotes, about the intense rivalries between Golden State cities and individuals to profit from the road-building enterprise. He also notes that with the advent of transcontinental railroads many of the earliest road builders' efforts were undone, largely because the railroads had ""the resources to blast and tunnel"" their way over mountain grades that would have been impassible for horse-drawn wagons. Though well written, this book, born of the author's doctoral dissertation, will appeal only to a specialized audience. Even so, it is a solid if modest contribution to 19th-century Western history.