Weird, I see two reviews with no mention of other authors.
Keep in mind, Penfield was a good archivist but his books aren't particularly helpful. They offer tons of very brief stories, usually less than 5 sentences, with not one scrap of bibliographic information to suggest where he got the information from. They're best use is breaking stories down by county which MIGHT give you at least an area to start researching but finding any sort of in depth material will prove difficult with the scraps he tosses out.
Thomas Penfield, H. Glenn Carson and Michael Paul Henson all penned different states using the same basic format with, unfortunately, the same shortcomings.