Vail has a lot of the traits that make a ski area great in March. It has a relatively high elevation, topping out at 11,570—not extraordinary for Colorado, but not bad—and 40% of its terrain faces north, which helps keep snow cold on hot spring days. The 40% number isn't exceedingly large, but that's forty percent of Vail, which is more than 5,000 acres, so that's 2,000+ acres of north facing terrain, which, by itself, is bigger than many major ski resorts, which will give skiers a lot of chalky snow to navigate deep into March. Much of that terrain is in the old part of the resort, the front face, not the back bowls whose terrain has a lot of awkward fall lines and fewer north-facing slopes.
Vail has one of the strongest snow profiles in Colorado, and that holds true in March. The ski resort usually receives strong March storms and can be a great place to spend a weekday chasing powder.
The north-facing terrain and size of this place can be an advantage for skiers who work hard and get out first thing in the morning. Sprint ahead of the late risers and mine the lifts farther from the base—which are really far from the base—because this is Vail and it's 5,400 acres.
What matters when it comes to snow for March skiing:
Ski areas with higher elevations and more northerly latitudes can keep snow colder when thawing temperatures in March or during warming events degrade other resorts' snowpacks. Aspects have the same affect, so the snow at a ski resort with more east or south-facing slopes will suffer more quickly as the sun grows stronger into March and the later spring.
For that reason, ski resorts with more north-facing terrain will be able to shelter snow more thoroughly into and through March. The most important factors for good snow preservation in spring tend to be elevation and north aspects, so the ski resorts with the highest elevations and the highest percentage of north-facing slopes tend to be those that preserve their snow best. More explanation on this topic can be found on our snow rankings page.
Lots of east and south exposures coupled with cold temperatures at night can put ski slopes into a nasty freeze-thaw process, wherein the ski resort becomes an ice rink overnight and doesn't revert to being skiable until the sun thaws things out. If the sun doesn't come out, however, skiers can be stuck with terrible conditions for days on end.
So, quite simply, in March, look for resorts with high elevations and high percentages of north-facing terrain (~50%+).