You step into a portal through time, onto glorious vistas that seem to mutate in the wind yet remain all of a grand piece, all of America. Somewhere amid the 19th century, you stand on a rocky outcrop, a stunning scene unfolding at your feet. The Hudson River rushes outward, past the stately Palisades cliffs, winding north into the Catskill Mountains. Travel further north by steamboat you reach Lake George, which Thomas Jefferson called "the most beautiful water I ever saw." And beyond, the Adirondack Mountains, the wellspring of the mighty Hudson.

Or head west by water, following the Mohawk River to the new and daringly built Erie Canal, an extraordinarily long human-made waterway, cut through limestone and mountains, across New York state to Buffalo and the Great Lakes beyond.

What you see along these waterways is vast and teeming: limpid lakes, unfettered wildlife, wary Native Americans, muscular rock formations and hoary, densely vegetated backbones of the earth, some reaching into the clouds. You see what America’s first generation of truly original artists saw and depicted – The New World in all its wild, rugged majesty – with humanity encroaching.

The artists would be known as The Hudson River School. The Milwaukee Art Museum’s "Nature and the American Vision: The Hudson River School" provides Midwesterners with an unprecedented experience of the nation’s first original artistic movement. If you were truly back in 1850s – traveling with these New York-based painters, poets and writers – the journey would be arduous. But today we see their bounty as art radiating historic experience, living nature.

"These extraordinary paintings overwhelmed 19th-century audiences with both their beauty and the razor-sharp commentary culture politics," said Brandon Ruud, curator of American art at MAM. "The art helped shape America and its identity."

The exhibit of nearly 50 works, many of monumental scale, come from the storied collection of The New York Historical Society and opens today with a run through May 8. This is the only Midwestern showing before the paintings return to New York. The visually sprawling yet easily traversable show climaxes with Thomas Cole’s ambitious five-painting series, "The Course of Empire," which arrives after a six-month showing at The Louvre in Paris, where it was reportedly the highlight of the city’s art season.

Ruud’s mounting of the show is big picture rather than pedantically chronological. We see from a contemporary standpoint the continent-spanning scope of what The Hudson River School wrought. So, one of the most powerful canvases we first encounter is Thomas Hill’s 1865 "View of Yosemite Valley, California."

Two horse-mounted explorers peer into one of North America’s most hallowed vistas, a great canyon guarded by gigantic sheer walls that still capture the imagination today, such as Half-Dome and El Capitan. Yosemite Valley, bathed in a glowing mist, reflects the atmospheric aura John Muir dubbed "The Range of Light," the vast Sierra Nevada range that includes Yosemite.

However, to get to Northern California, early travelers needed to cut through the ominously treacherous Donner Pass. In November of 1846, a brutal blizzard in the mountainous gulch blasted 81 emigrants trying to reach California, forcing them to spend the winter there. Only 45 survived to reach California, and some resorted to cannibalism.

One of the Hudson School founders, Albert Bierstadt, brilliantly captured the tragic locale’s awesome presence in "Donner Lake from the Summit" (1873). A god-like sun and the luminous Rocky Mountains in the distant background lead easily-imagined travelers through cloud cover to the foreground – the enveloping shadows of Donner Pass, a cruelly-carved wind tunnel that defiantly engulfs any traveler with its hulking peaks and forbidding cliffs. This writer traveled through Donner Pass last year and, even by car, it remains a daunting experience.

Meanwhile, the exhibit circles you back east to Thomas Cole’s serene "Catskill Creek, N.Y." with superbly rendered silhouettes of the North and South Mountains in gorgeous early autumn, with clouds dappled by the sunset and buoyant foliage just turning to gold. Paintings like this helped inspire the so-called American Grand Tour, in which educated urban residents dared increasingly venturesome trips into the mighty scenery unfolding westward.

The convergence of nature’s revelations and newfound artistic ambition prompted painter Asher Durand to declare a sort of artistic manifesto: "Why should not the American landscape painter, in accordance with the principle of self-government, boldly originate a high and independent style, based on his native resources?"

Indeed they did. Almost invariably these artists extended European-based training by applying carefully observed details of America’s brawny "unspoiled nature," working either on studio-bound sketches or completing their ambitious canvases on sight, en plein air. This extended, concentrated exposure "offered opportunities for spiritual reflection in renewal – what Durand called ‘lessons of high and holy meaning,’" writes Linda Ferber, director of the New York Historical Society, in her essay for the show’s catalog.

Affiliated poets and writers, such as Washington Irving and James Fenimore Cooper, also captured the "savage grandeur" of natural America, and one painting in the show, Cole’s expressionistic "Romantic Landscape (Last of the Mohicans)" depicts the setting of a crucial scene in Cooper’s famous novel "Last of the Mohicans," where the heroine Cora and her Mohican lover both die.

As the Hudson River School grew, contemporary American writers from the same New York/ England region greatly expanded the scope of American literary style and sensibility, in the so-called American Renaissance. Herman Melville, Nathaniel Hawthorne, Ralph Waldo Emerson, Walt Whitman, Emily Dickinson and Henry David Thoreau transformed American literature, doing justice to the implications of creative freedom that America’s independence and natural resources and beauty proclaimed.

Among America’s most breath-taking natural phenomena is "Niagara Falls," and Louisa Davis Minot captured the stupendous, crashing hydraulic cauldron of the world’s largest waterfall in her 1818 canvas. On the edge of Niagara Gorge below, a Native American stands, arms akimbo, in proper awe, while various white folks encroach the scene with other thoughts. This is long before Niagara became the heavily-developed tourist attraction it is today.

Indeed the infiltration and impact of civilization upon nature is the theme of Thomas Cole’s monumental, speculative five-painting series, "The Course of Empire" (1801-1848) which climaxes this extraordinary exhibit. It begins with a stunning scene, "The Savage State," in which a dagger-like rock promontory seems to trigger a black maelstrom of untamed natural energy. The next four paintings take the exact same setting through the rise and fall of a Roman-like civilization. Curator Ruud says Cole was a political conservative who feared a "mobocracy" of unchecked human democracy would be its downfall, as suggested in the Sodom-like fourth painting "The Course of Empire – Destruction."

Yet it remains up to the viewer to interpret the forces fully at play. The term "empire" does historically imply eventual political overreach, so how this occurs – then and today – compels contemplation of Cole’s soberingly apocalyptic time-lapse epic. The spear-like rock peak endures to the end.