When the Anderson Collection at Stanford University opens to the public on Sept. 21, it will be an anniversary of sorts. It was a half century ago almost to the day that a life-changing notion dawned on Harry W. and Mary Margaret Anderson while they visited the Louvre Museum in Paris for the first time. So utterly captivated were the Atherton couple by the modern works they viewed there–as well as at the nearby Jeu de Paume museum–they agreed on the way home to begin collecting great art.

Their venture started boldly and never waned. Early acquisitions included works by artists such as Pablo Picasso, Henri Matisse, Georgia O’Keeffe and Marsden Hartley. The couple, both born on the East Coast, had the wherewithal to indulge this passion; he was the co-founder of a food-service company so successful it was eventually purchased by the Marriott Corp.

In 1969, Harry and Mary–better known by their nicknames of “Hunk” and “Moo”–decided to narrow their focus. They would collect only post-World War II American art. That meant masterpieces by the likes of Robert Motherwell, Richard Diebenkorn, Jackson Pollock and Helen Frankenthaler.

For quite some time the Anderson Collection has been considered one of the most important private assemblages of 20th-century American art anywhere. Now, Stanford has a gorgeous new showcase for the gift of 121 paintings and sculptures from the core of that collection. In addition to Hunk and Moo, the gift comes from their collaborator and only child, daughter Mary Patricia Anderson Pence, also known as “Putter.”

Eighty-six artists are represented, among them Mark Rothko, Philip Guston, Wayne Thiebaud and Joan Mitchell, joining Motherwell et al. The crown jewel is Pollock’s horizontal drip painting “Lucifer” (1947), one of his most important works. The Andersons are said to have turned down an offer of $50 million for “Lucifer,” made in the mid-1990s by music mogul David Geffen. The canvas that once hung over Putter’s girlhood bed is easily worth twice that now.

All these treasures have been recently transferred to the stunning yet low-key Anderson Collection building right next to the Cantor Arts Center on campus. It’s the latest facility to join the school’s arts district, which also includes the Bing Concert Hall that opened last year. The 30,000-square-foot, $36 million structure is a “bespoke building,” according to designer Richard Olcott of the firm Ennead Architects. It was inspired by the Andersons’ own California ranch house–a series of interconnected spaces where gigantic art can be displayed with ease.

At Stanford, those spaces in the second-floor gallery are exceptionally inviting, just as one might imagine it would be.

Each work represents a movement in art and is arranged accordingly: Bay Area Abstraction, for instance, or New York School–which anchors the collection and includes “Lucifer”–or Post-Minimalism. Some of the sculptures, at least, will make you grin, if not laugh out loud. A piece in the Funk area titled “Hoarding My Frog Food” (1982), by David Gilhooly, is a tottering tower of toads, bread, buns and…toothy beavers.

Prior to their epiphany at the Louvre, Hunk and Moo had had no formal art education. Once they decided on their new mission, however, the Andersons eagerly absorbed art history and learned about the individual artists whose work they collected. The couple also turned to experts at Stanford, principally artist and professor Nathan Oliveira, as well as Albert Elsen, art historian and an authority on the sculptures of Auguste Rodin.

In 50 years, the Andersons have made a staggering 2,000 or so acquisitions. Before their gift to Stanford, the family had already bestowed numerous works to the San Francisco Museum of Modern Art–a top-flight group of Pop Art paintings, among others–and the Fine Arts Museum of San Francisco (655 graphic works). Their largesse to the Bay Area will be enjoyed and studied by many for years to come, a legacy that will be the couple’s personal masterpiece.

The Anderson Collection at Stanford University, 314 Lomita Drive, is located next to the Cantor Arts Center. Public opening Sept. 21 10 a.m. to 8 p.m. Reserve free timed tickets atanderson.stanford.edu. Beginning Sept. 22, both the Anderson Collection and the Cantor Arts Center will be open six days a week: Wednesday to Monday 11 a.m. to 5 p.m., Thursday 11 a.m. to 8 p.m.