The title of this book Lighting Out for the Territory by Roy Morris, jr. refers to the last paragraph in The Adventures of Huckleberry Finn when Huck reckons that it's time "to light out for the Territory ahead of the rest", which is exactly what Clemens himself did in July 1861. Clemens had ridden as a guerilla maurader for the Missouri militia in a locally formed group in the very early days of the Civil War called the Marion Rangers. They never saw any real action, but his brief stint with them, plus the ever present chance he could be drafted by either side, Union or Confederate, to pilot a gun boat, made the mostly neutral West look inviting.
His brother Orion had been appointed as Secretary to the Territorial Governor of the newly created Nevada Territory. Orion invited Sam to go along to share expenses. From this happenstance beginning one of America's great writers was born.