One of Denver’s first microbreweries, and the namesake behind what became a multi-state chain of well-recognized brewpubs, has closed after 35 years on the Sixteenth Street mall.

Located on the first floor of what was once the Prudential financial services building. Rock Bottom was founded in 1991 by Boulder restaurateur Frank Day, who had opened the Walnut Brewery in his hometown a few years earlier. He named it Rock Bottom as a cheeky reference to Prudential’s famous tagline, “Get a piece of the rock.”

On Monday, a sign on the door read: “Unfortunately, we have permanently closed. Thank you for allowing us to serve the Downtown Denver community.”

An email to the company’s ownership group wasn’t immediately returned.

Rock Bottom grew to become a formidable institution in itself, catering to office workers and nighttime crowds who could watch their beers being made while they dined – a novel concept at the time, when only a few other breweries dotted Denver.

Over the years, Day — who died last year at the age of 93 — expanded, opening Rock Bottom locations throughout Colorado and the rest of the country. In 2010, he sold the company alongside the equally famous Old Chicago Pizza & Taproom chain (which he’d also founded), as well as other restaurants, to a Tennessee private equity firm called Centerbridge Capital Partners.

The company was sold two more times over the next dozen years and is now owned by another private equity group called Kelly Operations. Rock Bottom closed its Colorado Springs location in April, and now has just five locations, according to its website, three in Colorado, one in Illinois, and one in Boston.

Although it became part of a chain, losing some of its individuality in the process, Rock Bottom began as a feisty competitor to Wynkoop Brewing, which Colorado Sen. John Hickenlooper and his business partners had opened in 1988. It was the recipient of dozens of medals and awards, both at its downtown brewery, 1001 Sixteenth St., and at many of its other locations, and a pioneer in an industry that now includes more than 9,000 breweries nationwide — more than 400 of those in Colorado.

When Day died last year, Hickenlooper told The Denver Post: “[Day] took every one of our ideas and made them so much better. At Rock Bottom, the hot food was hotter and the cold food was colder. When Frank opened Rock Bottom, it changed the face of brewpubs everywhere.”

Subscribe to our new food newsletter, Stuffed, to get Denver food and drink news sent straight to your inbox.