Memorial Day Memoir @ Mammoth Mountain, CA – 2018 Even on the driest of years, Mammoth Mountain consistently remains open until โat leastโ Memorial Day (late May.) On massive years, they run the upper lifts until Augustโฆyes, a non-glaciated mountain that runs lifts until August. If I recall correctly, the years of August 1995 & 2017 to name a few. On a normal year, the goal is run lifts through the July 4th weekend. Trip Report Casey Cane | May 23, 2019 0 Comments