Very obviously an early work, and a patchwork of Twain's experiences as he opted to mostly miss the Civil War by traveling into the then-territorial west of North America. This is very much a patchwork, and a long one at that: personal recollections are interwoven with tall tales, and occasionally peppered with some political incorrectness that's uncomfortable to read in these supposedly more enlightened days. The Mormon church and native Hawaiians bear the brunt of this, and Twain was not yet a refined enough writer (or person?) to let it move into parody: it just feels mean.
Still, Twain's embellishing touch is evident, and you can see the celebrated writer through the awkward passages. His travels by stagecoach are particularly enjoyable, and since I live in the area, I was personally pleased to read his impressions and recollections life in of Lake Tahoe and a young San Francisco, including experiencing a destructive earthquake. Like his silver-mining adventures, there are many worthy, entertaining parts to this book, but you must chip through some lesser material to get to it. The edition I read from Project Gutenberg
appears to be a full one, including a number of appendices.