Wolfhounds and Polar Bears: The American Expeditionary Force in Siberia, 1918–1920 

This book covers a lot of the same ground as other books on the topic, but that said, there was a lot of information here that I'd not seen in other sources...it often seems to be describing the same incidents, but from a different perspective or from a different source.  The book also includes more information about the American railwaymen serving in Russia, and tells much more about their challenges than most other books on this period.  So those are the good points; on the down side, the writing style is often very wooden and choppy, and so it it can be a bit of a chore to get through.