California's Mammoth Mountain is wrapping up its second-longest season after 275 days

The lifts at Mammoth Mountain in California will stop spinning Sunday after an incredible season spanning 275 days — the second-longest ski season in the resort's recorded history — and nearly 900 inches of record-breaking snowfall.

Tucked into the Eastern Sierra Mountains, Mammoth is California's highest ski resort at just over 11,000 feet. And though it's not unusual for the mountain to stay open into late spring, a nine-month season stretching into August has only happened two other times in the resort's 70-year history.

"This year on July 4th, almost the entire upper mountain was open. It was basically full go. That's very unusual," Tim LeRoy, co-founder of BluBird Communications and Mammoth Mountain spokesperson, told NPR.

The mountain was scheduled to open on Nov. 11, 2022, but early season snow storms, coupled with colder temperatures for snowmaking, allowed the mountain to open almost a week early on Nov. 5, according to Mammoth's Instagram posts.

However, the season's longevity was made possible due to atmospheric rivers that pummeled California over the winter. These corridors of concentrated moisture vary in size, according to the National Oceanic and Atmospheric Administration. But at over 1,000 miles long and an average of 250 to 375 miles wide, the agency says, the "average atmospheric river carries an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River."

And exceptionally strong atmospheric rivers can transport up to 15 times that amount, NOAA says, which condenses and falls to Earth as rain and snow.

Mammoth recorded 116 inches in December, which was higher than average, but nowhere near record setting. But a whopping 220 inches — or over 18 feet — fell in January, the mountain's second-snowiest January on record, according to the resort.

On several occasions the mountain received so much snow in so little time that the resort had to shut down. LeRoy said Mammoth staff spent countless hours digging out lodges and chairlifts, performing avalanche mitigation and more to try and open the mountain for guests.

"The real heroes here are the people who put the time into opening the lifts every day; it was a herculean effort," he said. "When you think of what goes into opening a mountain with that kind of snow, it's hard to wrap your mind around."

On March 30, Mammoth posted that a recent storm had set the resort's record for total snowfall in a season, exceeding 700 inches — over 58 feet. The resort recorded 715 inches at its main lodge at the end of the season, and nearly 900 inches, or 75 feet, at the summit.

The previous snowfall record at the mountain took place in the 2010-11 season, with 668 inches, or over 55 feet. The resort sees an average of 400 inches of snow annually.

What separated this year from past seasons, LeRoy said, is how well the snow held up as spring transitioned to summer. On June 21, Mammoth employee Justin Romano reported that the mountain still had a 70-inch snowpack at the base area. "And we are riding top to bottom. Don't think many other resorts can say that around the country," he said while being pelted with summer snowballs.

LeRoy said Mammoth was planning on closing sometime at the end of July, "but then when we got close to that we realized we could go a little further." On July 20, the mountain announced it would stay open until Aug. 6, making it the second-longest season in the resort's history.

Mammoth's longest season took place nearly 30 years ago, when it was open from Oct. 8, 1994, through Aug. 13, 1995, having received 540 inches of snow over the season.

Though mountain operations are shutting down Sunday, the resort won't stay dormant for long, having already announced a planned opening of Nov. 11.

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