Rare Georgia O'Keeffe painting found in closet of NYC apartment, to be auctioned for at least $3 million

"Holy cow."

That was the first thought a woman, only identified as Betsy, had when she found out that her aunt was the owner of a rare Georgia O'Keeffe painting.

The 1930 painting, titled "Near Abiquiu, New Mexico I", depicts an undulating landscape of New Mexico. It hasn't been seen publicly for decades.

Betsy, who spoke to CBS News New York on the condition of remaining anonymous, says the rare piece of American history had been sitting in a closet in her aunt's East Village apartment since the 1980s.

Originally purchased in 1963, Betsy says her aunt owned many valuable pieces of art throughout the 1970s, never married, had no children, and lived a successful, cosmopolitan life as a career woman.

The painting was only recently revealed to the family at the end of her aunt's life when arranging her affairs. Betsy says the aunt had once displayed the painting in her apartment then put it away after noticing untoward interest in the piece from a party guest.

A lot of work goes into verifying a discovery like this is real.

"We certainly use just a visual analysis of looking at the painting, looking at the styles, how the brush strokes may match, how other O'Keeffe's appear that we've known that we've sold," said Tylee Abbott, the head of American Art at Christie's New York. "But also, O'Keeffe is very well-documented with a catalog resume that published all known works of her. This work, of course, appears in the addendum of that as kind of 'unlocated.'"

"Unlocated" until now.

"It was last known from a photograph in 1931 that Alfred Stieglitz took of her of a gallery exhibition," Abbott said. "We actually have documented the original bill of sale from O'Keeffe's Downtown Gallery in 1963, when the current owner purchased it. So, all of that tied together is a surefire confirmation that this is indeed a genuine Georgia O'Keeffe."  

Now, it will be sold for at least $3 million at Christie's New York auction house's 20th Century Evening sale on Nov. 17.

Before it goes to the highest bidder, New Yorkers can see the piece for themselves for free from Nov. 7-17 at 20 Rockefeller Center in Manhattan.

The auction and public exhibition period will also feature the works of Pablo Picasso, Jean-Michel Basquiat, Claude Monet, Wassily Kandinsky and Andy Warhol.

Called by some as the "mother of American modernism", O'Keeffe was born to dairy farmers in Wisconsin and dreamed of being an artist at the age of 10. Known for her charcoal drawings, abstract paintings of New York City skyscrapers, and depictions of the nature, particularly in the American southwest, she is considered one of the most important artists of the 20th century.

The painting for sale is estimated to have been finished early into her travels to New Mexico, a place she would eventually call home and where a museum is dedicated to her in Santa Fe.

"O'Keeffe goes to New Mexico in 1929, and this picture is from 1930, so it's the ground floor of her inspiration at that time of first experience in New Mexico, and the landscape and the atmosphere. And she is very vocal about, in her writings and things, about how impactful it was on her. I think you get that in this picture," Abbott said.