Paintings depicting the American West from William Koch collection heading to auction in NYC

Christie's auction house will offer a large group of paintings depicting the American West from the collection of billionaire businessman William Koch (kohk).

The May 21 single-owner sale of 69 paintings in New York City is expected to bring over $13 million.

The offerings span from the 19th century to modern times and represent the most important artists of the genre. They include Thomas Moran, Frederic Remington and Henry Farny.

Among the highlights is Moran's "Green River, Wyoming." It's estimated to sell for $6 million to $8 million.

Moran traveled to Green River City for the first time in 1871. He was on a surveying expedition of Yellowstone to illustrate an article for Scribner's Monthly magazine. The painting has never appeared at auction before.