The fire that consumes Tamar’s world is more than a sacrificial fire offered up to “magic horror away.” It is a fire of primal yearning. When Tamar says, “I have my desire,” that narcissistic lust is what aches to set her family’s house ablaze, and correspondingly, in Apology for Bad Dreams, it is a fire—represented by the flammability of the California coast—that ignites Jeffers’ world over and over again. The poem returns to the notion of return, and then it returns again (SP 143–4):
… Beautiful country burn again, …
Burn as before with bitter wonders, …
… I know of no reason / For fire and change and torture and the old returnings.
… the ever-returning roses of dawn.
Jeffers adopted the notion of eternal return from Friedrich Nietzsche, though Jeffers took it more on faith—as objective fact—than did Nietzsche. Nietzsche developed the concept primarily as a thought experiment, though it seemed he wanted to believe in it ontologically, objectively. Nietzsche seemed to have got the idea from his “great teacher,” Arthur Schopenhauer (Nietzsche’s wording on the topic reflects that of Schopenhauer). Some Jeffers scholars have managed to make quite a big deal of eternal recurrence, citing without justification obscure sources such as Ishtar, sometimes without even mentioning Nietzsche! The neglect of Schopenhauer, probably due to a simple ignorance of philosophy among a few English professors, is just as noteworthy.
Tamar’s “desire” to influence men and events might be said to represent Nietzsche’s will to power, though it seems to begin as something more primitive and “half-innocent”: a will to life, represented by the animal will to reproduce that operates more deeply than Nietzsche’s more humanistic, derivative notion. Will as thing-in-itself, deep sexuality, and unconscious thought call Arthur Schopenhauer to mind. This contrarian and anti-authoritarian, who had such a profound influence on Nietzsche and—without attribution—on Sigmund Freud, has been mentioned before in reference to Jeffers, but no treatment of Jeffers appears to have done more than skim the surface of Schopenhauer’s thought.
Radcliffe Squires, in his 1956 study The Loyalties of Robinson Jeffers, criticized the then-prevailing belief that Jeffers was a somewhat dogmatic Nietzschean. As an antithesis, Squires proposed that Jeffers’ thought was more akin to Schopenhauer, though Squires regarded Jeffers as a materialist and stopped short of classifying Schopenhauer as an “influence.” He also stopped short of providing adequate argumentation.
Squires acknowledged that Jeffers was more immediately influenced by Nietzsche, but that Jeffers’ response to Nietzsche was mostly antagonistic—though he was quite the Nietzschean with respect to eternal return, the unconscious, and "Freudian" repression.
The case for Jeffers’ kinship with Schopenhauer is not to be made on the metaphysical grounds of the German philosopher’s Idealist pedigree, yet even to label Schopenhauer as an Idealist is to oversimplify him. Schopenhauer did speak in the language of Idealism, but what he did with it took him far from Kant.  Schopenhauer, notably influenced by Scottish empiricist David Hume in his ethics of compassion, took the metaphysics of Kantian Idealism and made German thought ache with physicality and unconscious sexuality. Though he adopted the view that the world as it appears is a construct of the mind, he arrived at the radically materialistic conclusion that states of the mind are states of the brain. In this context, the dissolution of Old Martial’s consciousness (in Cawdor) is somewhat friendly to Schopenhauer’s biological view of the mind.
“Idealism,” in this context, is not a doctrine that posits “the world as idea,” but rather the doctrine that things as we perceive them exist only in our minds. But this does not mean that there is no external reality. The point of the Idealist is only that our minds cannot understand reality fully “in itself.” Schopenhauer believed in reality as “thing in itself,” but as an “Idealist” he did not believe that reality equals our perception of it. Furthermore, he did not believe that reality is fundamentally mental; rather, he postulated that reality corresponds more to “will,” as a sort of subconscious, physical and blind urge that unravels into our “reality” of objects in space and time. Schopenhauer was known to see the best representation of “will to life” underlying the human animal to be the genitalia. It would be a great error to suggest that Schopenhauer believed the world to consist fundamentally of some sort of incorporeal “idea.”
Schopenhauer’s “world as will,” is a largely biological notion that expresses itself in subconscious urges, in cycles of craving and brief satisfaction, not entirely alien to the Logos-fire of Heraclitus, which that Greek philosopher described as “craving and satiety,” and not altogether dissimilar to Jeffers’ own recurrent fire:
Someone flamelike passed me, saying, “I am Tamar Cauldwell, I have my desire,” … 
Modern physics, by the way, is not terribly estranged from Schopenhauer’s Kantian view, in that modern physics has undergone enough conceptual revolutions and revisions to see that the physical world seems to change radically as our models of it change. As Werner Heisenberg put it, “atoms are not things.” Atoms are certainly real in that they are not wholly objects of consciousness, but they are at the same time objects of our models of thinking. What an atom “is,” that is to say what it is to us, has become rather difficult to express over the last century or so. Atoms are, just like anything else, reality as seen through our eyes (or instruments). They are not things, but rather “objects:” objects of consciousness; in other words, “phenomena.”
These phenomena, for Schopenhauer, do not derive from some abstract idea or pantheon of ideas. Schopenhauer was a thorough-going empiricist, which is to say that he believed concepts (science) to be secondary to perceptions.
Having said all this to clarify and justify the philosophy of Schopenhauer, and as well to point to a strong connection between him and Jeffers, I do not propose that Jeffers was a follower of the radical German philosopher’s “Idealist” metaphysics. Jeffers was a realist. He was a realist in the sense that he believed that nature can be perceived as it is, or in other terms, that God can be known. In this sense he was perhaps in good standing with Einstein—as well as any dogmatic theist. Jeffers did not believe the senses ought to be fully trusted,  yet he believed that the world that we perceive is indeed the world as it is.
Jeffers had not always been very clear-eyed on the question. In the 1927 poem Credo, Jeffers conceded that what we see of the world is in our mind, but he insisted that there is a real world beyond our senses:
I think that the ocean in the bone vault is only
The bone vault’s ocean: out there is the ocean’s; ... 
The question, of course, is then can we see the ocean’s ocean? If the ocean as we see it is only in the mind, in what sense can the mind understand the reality of the ocean? This is a critical question, for what point is there in discussing what is beyond our understanding? What point is there in even saying that it exists?
There are other differences between Jeffers and Schopenhauer. Jeffers, though not a theist wrote frequently of God, whereas Schopenhauer was a strict atheist. Schopenhauer was a philosophical pessimist, yet he believed that good exists in the world in the form of human compassion. Jeffers, in contrast, professed little admiration for anything human, and saw salvation in the “confidence” of the eternal “inhuman.” Still, there is much in common between the two.
The link between Jeffers and Schopenhauer passes through the filters of Nietzsche and Freud, but it can be easily identified in Jeffers’ treatment of the unconscious, sexuality, repression, human exceptionalism, pessimism with regard to human consciousness, and eternal recurrence.
Sigmund Freud denied having been directly influenced by Schopenhauer, though he seemed to have taken his core ideas from Schopenhauer, but Freud had a myth of originality (and a contempt for philosophy) to defend. Recent scholarship has questioned Freud’s claim to originality in this regard. But notwithstanding Freud’s own suppression of his scholarly influences, Schopenhauer had injected an idea of the unconscious, along with a new emphasis on sexuality, into the intellectual æther of Germany well before Freud commenced his fetishizing of the same.
Schopenhauer, as psychologist of the will, is the father of all modern psychology. From him the line runs, by way of the psychological radicalism of Nietzsche, straight to Freud and the men who built up his psychology of the unconscious and applied it to the mental sciences
—Thomas Mann 
And here, from the proverbial horse’s mouth:
The intellect remains so much excluded from the real resolutions and secret decisions of its own will that sometimes it can only get to know them, like those of a stranger, by spying out and taking it unawares: and it must surprise the will in the act of expressing itself, in order merely to discover its real intentions.
—Schopenhauer, World as Will and Representation II
What one may not have read directly from Schopenhauer, one may have very possibly read from Schopenhauer’s student and detractor, Nietzsche:
Man, like every living being, thinks continually without knowing it; the thinking that rises to consciousness is only the smallest part of all this – the most superficial and worst part – for only this conscious thinking takes the form of words, which is to say signs of communication, and this fact uncovers the origin of consciousness” 
The Gay Science, V: 354.
Next, we have the common theme of renunciation. Jeffers’ primary message is that human suffering is best mitigated by means of detachment from human self-consciousness, whereas Schopenhauer’s solution was renunciation of the particular self.
It is the gleam of silver that suddenly appears from the purifying flame of suffering, the gleam of the denial of the will-to-live, of salvation. 
Schopenhauer, it happens, lumped men and animals together, though he distinguished man as more conscious and therefore more miserable. Jeffers would later make the same assertion.
In like spirit, Jeffers wrote (SP 676):
We must uncenter our minds from ourselves;
We must unhumanize our views a little, …
Regardless of what Jeffers thought of Schopenhauer, this “inhumanist” philosophy of Jeffers is highly reminiscent of Schopenhauer’s Western cousin of Buddhism, though Jeffers seems to present itself as the stark Theravada to Schopenhauer’s more compassionate Mahayana. If Jeffers wasn’t directly influenced by Schopenhauer, we do know that he was influenced by Nietzsche, and by the way, that English “inhumanist,” Thomas Hardy, who most certainly was influenced by Schopenhauer. Curiously, all four of these men were noted for their sensitivity to animal suffering. Schopenhauer was quite outspoken on the matter: 
Compassion for animals is intimately connected with goodness of character, and it may be confidently asserted that he who is cruel to animals cannot be a good man.
Because Christian morality leaves animals out of account, they are at once outlawed in philosophical morals; they are mere ‘things,’ mere means to any ends whatsoever. They can therefore be used for vivisection, hunting, coursing, bullfights, and horse racing, and can be whipped to death as they struggle along with heavy carts of stone. Shame on such a morality that is worthy of pariahs, and that fails to recognize the eternal essence that exists in every living thing, and shines forth with inscrutable significance from all eyes that see the sun!
Proceeding almost inductively, one can see that Schopenhauer was the first Western philosopher to reject human exceptionalism. One recent article observes:
Schopenhauer’s point was that “dignity of man” came to be a signal of an in-group, not really conveying any meaning, but reassuring and encouraging the proponents of human exceptionalism. In doing so, Schopenhauer anticipated modern critics who find the term vacuous. 
This “dignity of man” is Kant’s term. Kant believed each human to be an “end in itself,” yet he saw animals as a means to any end; a view that Schopenhauer found “revolting” and “abominable.”
Where Jeffers saw human self-consciousness as the problem, Schopenhauer saw the human problem as the Will exacerbated by consciousness. It might be said that where Schopenhauer saw—or felt—a universal Will, Jeffers saw the beauty of God, and the image of a fire. Whereas Schopenhauer posited a Will burning within, Jeffers envisioned a fire, just as that Greek materialist Heraclitus had seen fire as that ultimate substance. Jeffers was nominally more of a materialist than was Schopenhauer, but Jeffers’ notion of divine beauty was in its cruel sublimity more akin to Schopenhauer’s Will than one might guess.
Radcliffe Squires recognized that Jeffers was first and foremost a materialist, though Squires recognized an idealist thread in Jeffers’ theology. Although Jeffers did not present himself as an idealist in the Kantian tradition, his attachment to notions of God, transcendent beauty, the sublime, and panpsychism might betray a an implicit idealism. Jeffers’ characterizations of his God are sometimes so detached from ordinary reality that it becomes hard to classify Jeffers as a true pantheist. God, for Jeffers, is no mere metaphor for the universe but rather a religious preoccupation. Jeffers’ theology, arguably one of panentheism,  occasionally seems downright Neoplatonic, hardly distinguishable from the mystical theology that I was introduced to as a young monotheist. “Nature is God’s Will,” I was taught,  though precisely what I was to learn from nature seems to have been determined by scripture.
Tragedy as Therapy
To Schopenhauer, tragedy was the highest form of poetry because it served as a kind of cathartic cleansing with a potential to free its audience from bondage to the Will, whereas Jeffers’ narratives resemble cathartic rituals wherein something deep within certain characters threatens to well up and ignite waves of mayhem. Their functional objective is Schopenhauerian: liberation from human self-consciousness. Their characters seem like puppets or archetypes rather than human beings, so much so that Jeffers’ narratives lack empathy and thus make poor “tragedy,” though a deep, universal affliction seems to lurk within them.
Schopenhauer was no pantheist (and certainly no Calvinist); rather, he was an atheist who regarded pantheism to be just as inane as “human dignity.”  He probably would not have acknowledged Jeffers as a disciple, but he would have likely recognized his own thought in Jeffers’ cyclical metaphysics, his Inhumanism, and his textbook Freudianism.
Having thus argued that Jeffers and Schopenhauer were kindred spirits (with significant exceptions), I do not maintain that one must understand Schopenhauer to appreciate Jeffers. At the other extreme, if one is going to claim with an air of academic authority that there’s some unbridgeable gap between the two, a preliminary read-through might be advisable.
 Snow, Dale E. & Snow, James J. “Was Schopenhauer an Idealist?” Journal of the History of Philosophy, Vol. 29, No. 4. October 1991.
 SP 143
 Advice to Pilgrims; SP 579
 Credo; SP 147
 Young, Christopher and Andrew Brook. “Schopenhauer and Freud,” International Journal of Psychoanalysis. 1994 (75), 101-18.
 Mann, T. Speech given on the occasion of Freud’s 80th birthday. Essays of Three Decades. Canada: Random House of Canada Ltd., 1968. pg. 408
 Nietzsche, The Gay Science, V, page 354
 Schopenhauer, The World as Will and Representation, Book IV: "The World as Will: Second Aspect"
 Schopenhauer, Ueber die Grundlage der Moral (On the Basis of Morality), 1840.
 Calhoun, David. Human Exceptionalism and the Imago Dei. 2013
 Not to be confused with pantheism.
 “Tablet of Wisdom.” Tablets of Bahá’u’lláh Revealed after the Kitáb-i-Aqdas, 1978.
 Calhoun, David. Human Exceptionalism and the Imago Dei. 2013