waters flowing through depths, emerging far away

Devil's Gate, Wyoming
Frederick Piercy, 1853

Hershel Parker, Melville Biography: An Inside Narrative:

"To declare that Melville was interested in bodies of water—lakes, ponds, flowing water, waterfalls, confluences of rivers, and oceans—is to announce the obvious. But there was more. Melville was fascinated by, perhaps haunted by, feelings of being subterranean, in the orlop deck, in vaults, in passages such as Giovanni Belzoni wormed his way through, in depths below depths as in the Hôtel de Cluny in Paris. He was particularly intrigued by waters that went subterranean and emerged far away." (15)

"You stand upon one side of what seems a deep green river, flowing through mountain passes to the sea..." (Omoo)

Thus liberated, the river enters a vast sunburnt plain; and, as if to take a last farewell of the romantic ridge, runs five or six miles to the foot of the solitary Independence Rock, thrown out like a grim sentinel upon the desert's boundary; then, as if warned of the salt and lava desolation beyond, turns again, and hastens to join the Platte, to aid in the evident struggle before it, with all the rocky powers of chaos and volcano.

Having thus, as from impulse, surrendered name and identity, and the excited contest over, they emerge from the secret and sublime mountain passes, in dreary unity, upon the boundless flatness of barren plains,—though some fleeting enjoyment of flowery savannas succeeds— before both are lost in Missouri's dark and turbid flood.

Farewell to thee, then, sweet daughter of Mountain! Thou smile upon our mother's melancholy face! Go,— with thy bright and blithe innocence,—like many another victim;—go purling merrily when you may, ignorantly happy, to the dark course of thy destiny. Thus do the Fates spin our warped life-threads,—thus do we weave its chequered or sombre web! [earlier version, Sept. 1852: "...ignorantly happy, to the chequered course of thy destiny. Thus do the silent Fates prepare for our warped life threads their sombre woof!]

.... Silvery gleams attract our sight—there is water—it is the river! In the midst of its secret, fierce course, a sweet glen has tempted it to a gentle pause on its soft bosom. It is then a river valley! Truly, close to our right, through an unsuspected chasm of wondrous depth, the happy Platte, having been somewhere secretly united to Sweet Water, has come to meet us, as witnesses to its triumph, or sharers in the excitement of a pleasure tour. Lowly, but bright and joyous in its life of motion and cumulative power, it advances, courting first all sweet and quiet recesses—yet daring all opposition to its wilful course. How we watch it now! Yonder, it sweeps in curves of beauty;—but suddenly lost, we gaze conjecturing where it may next appear; unexpectedly, it has paid a smiling visit to a grim mound, that stands modestly far aside; satisfied, it comes forth to new discoveries;—a determined barrier seems opposed ; but carelessly yet, it sports in some little meadows which can scarce be seen. Then it advances more seriously to a green hill, which seems bent in homage. But no! Nothing less than the loftiest mountain of proud rock, must give it passage! and through a narrow—a sublime chasm, it fiercely rushes forth to new labyrinths beyond.

September 1852, Scenes Beyond the Western Border; and
Scenes and Adventures in the Army

Update:  This lavish personification of the Sweetwater River has also to do with, besides surprise emergings from depths and labyrinths, a preoccupation with the confluence of rivers, here the Sweetwater and Platte, with a gloomy anticipation too of another confluence, the inevitable merging of the Platte and Missouri rivers.

"Why would he not seek out confluences of rivers, since from childhood he had walked on the Battery, seeing where the East River and the Hudson (or “North River”) merged after they poured separately into the bay?"  (Hershel Parker, Melville Biography: An Inside Narrative)