Why? Because it gets too much snow during the winter months to operate. Yes, really!
When the resort opened in 2010, the snow depth at the summit was over 26 feet deep, according to Unofficial Networks. Winter operations were unable to take place.
They have to wait until the summer months to be able to get the lifts running and the pistes bashed.
It's only a small resort with three lifts - but plenty of Japanese shredders strap into their touring kit and hike up the the 5480ft peak to the top of Ubagatake.
It's not the best video we've ever seen but it'll give you an idea of what it's like to ride powder in Gassan, if you skip to 0.27.
Anyone fancy hopping on a plane this year?