The owner of a popular Philadelphia pizza restaurant died after an accident at a Colorado ski resort.

Frank Maimone, the owner of Rustica pizzeria in Northern Liberties, was skiing at Colorado's Steamboat Resort Saturday around 2:30 p.m. when he fell into a tree well.

A tree well immersion accident occurs when a skier or rider falls into an area of deep, loose snow and becomes immobilized and suffocates, according to the National Association of Ski Areas.

Maimone was found unresponsive on a black diamond, or expert, trail.

He was taken to the UCHealth Yampa Valley Medical Center in Steamboat Springs, Colorado, where he was pronounced dead. He was 53 years old.

The Steamboat Ski Patrol performed CPR throughout Maimone's transport from the resort to the hospital, officials said.

There was no visible trauma but a cause of death had yet to be determined, the coroner said.

An autopsy report was expected to be released Monday.

Steamboat Ski & Resort Corp. did not immediately return a call requesting additional information.

Rustica, located on 903 North 2nd Street in Philly's Northern Liberties neighborhood, was voted the best non-gourmet pizza restaurant by Philadelphia Magazine in 2010.

The restaurant was established in 2001 and was one of the first of its kind in Northern Liberties, according to its website. The business is also involved in community events and organizations, including PAWS, Fishtown SPCA and Girls Rock Philly.