David Rothenberg lists whales among his contributions to Bass Lines / Border Lines, an arresting credit for a record made in the Dance Hall in Arivaca, Arizona, near the U.S.–Mexico border. The opening piece, “Jaguar through the Wall,” puts that border in the path of an animal with its own reasons for crossing. By the 17-minute finale, “Lives of the Desert Whales,” a humpback has joined Rothenberg and bassist Glen Moore. Rothenberg was 18 when he spent a summer studying with Oregon, the group Moore cofounded with Ralph Towner, to whose memory the album is dedicated. He had been listening to Moore for decades by the time of this recording, and in an interview he mentions how closely a humpback’s song can resemble a bowed double bass. With Moore in the room, the resemblance is just as intriguing the other way around, and you start to wonder how much ocean a bass can hold.

The jaguar is already in motion when we arrive, and the immediacy of the playing gives us no time to craft arbitrary expectations for the improvisatory wonders about to ensue. Upright bass and bass clarinet are griots of subterranean (if not submarine) proportions, versed in whatever passes between a root and the rock it spends its life prying open. Moore’s slides and Rothenberg’s reptilian dances make for a gorgeous pairing, their lines doubling back across ground that each has opened for the other. Beneath the bubbling surface is a deep sense of structure, audible in how much time the players give a delicate passage to find its footing. Their mastery has everything to do with the way they listen, and you can hear it when one catches the tail of the other’s phrase and lets it go.

The arco strains and harmonically infused glissandi of “Coati Mundi” bring us into more crystalline territories, into caves hewn by the slow drip of mineral. The navigation is both external and internal, concerned with the contact of feet to earth even as it works through crevices in search of a softer place. The restraint here is striking, each slip of pitch exposing another translucent layer in what had seemed an indivisible darkness. The title track opens with a superbly articulated bass solo, and the release is so consummate that even Moore seems to have been overtaken by it. Rothenberg’s monologue rides the wave of a backgrounded reverb, charting a passage through time as a physical substance to be felt with the soles of the feet. When an echo lays another floor beneath a word that has just touched down, you can almost feel the ankle adjust.

As the duo comes together, grittier doctrines take shape only to be sliced by the blade of “Your Final America,” which brings cross-sections of the heart into focus. I hear a whisper pitched directly into the ear of an ungracious automaton whose instincts are wired for profit and exploitation. There’s an unnerving intimacy to the address, as though an apparatus of extraction might be persuaded to grow a conscience if someone spoke into it gently enough. Whatever tenderness our storytellers can recover from the encounter, they carry forward in the form of pollen, which has always depended on being taken somewhere it had no means of reaching on its own. Even the whimsically titled “A Lizard War” is a delicate conflict, one that creates as much as it destroys. Its scrapings and postures are part of a mutual language in which each contributor is an equal force, and what survives the scuffle is the possibility of succumbing just as quickly to the next encounter.

In “Lives of the Desert Whales,” the humpback’s song emerges as an organic sonic child and, in the same breath, a parent shepherding the space-time continuum through its own coming of age. The growling compass the musicians have been carrying through the desert now swings toward a creature for whom any line on a map must seem a remarkably provincial invention. The lines Moore and Rothenberg have been drawing all along are measured in breath and in the length of a bow stroke or finger strum. I imagine a fossil hunter lifting a human cochlea from an Arizona outcrop and cataloguing it as the shell of an extinct marine animal. There would be a certain justice in the error, for the most intimate thing that fossil could reveal about our species would be the shape of what once lived inside us without ever becoming ours.