Summary: MacLane's last, deepest book.
To adapt my comment on I Await the Devil's Coming (also published in Melville House's Neversink series): as a long-time researcher and publisher of MacLane's work, I welcome Melville House's publication of this 1917 classic, insufficiently-understood in her time and unsurpassed to this day in communicating the inner reality of a complex, surging, sui generis spirit.
As I remarked in a recent MacLane anthology: MacLane's final book was her testament in every way and concludes the evolution begun in "I Await the Devil's Coming". She had vowed to explode out into the world from Butte, and now she turns within and ranges through her internal world. Taking her second book, the static and neutral-toned "My Friend Annabel Lee" as center, the three books balance neatly.
Written from 1911 to 1917, "I Mary" seems both impromptu and outside of time. While superficially emulating the dated-entry format of "Devil's Coming", it positions the reader in the most intimate contact MacLane would ever permit: we are with her inside herself, in - except for the first and, movingly, a later entry - an eternal tomorrow. The martial narrator of "Devil's," who stood off and upbraided the world, is long-gone; the two personae in "Annabel" have seemingly fused in order to problematize the inner world. Here, MacLane seems to say: watch my givens as they pass; below these I will not go, and they are neither good nor evil - they simply are. Yet her humor - dry, sly, strongest at her (as she might say) seriousest - never deserts us.
It is not known if MacLane read Nietzsche - her iconoclastic sometime supporter H.L. Mencken was an early American advocate, and he'd read Max Stirner - but if "I Await the Devil's Coming" was an exercise in self-assertion, "I, Mary MacLane" ventures into a self-criticism probably entirely uninfluenced by Freud.