Below is A-Basin’s policy off their website.

A decision to have uphill access open or closed will be made and posted by 6:00am daily.

Arapahoe Basin Uphill Access: Uphill access by means of skinning, snowshoeing and hiking has gained popularity at Arapahoe Basin in recent years. The ski area welcomes and supports individuals seeking to exercise and enjoy the quiet mountain setting. Mountain users can help preserve this opportunity by following these simple guidelines:

1.You are required to have a complimentary uphill access pass. This pass is available at the Season Pass Office during operational hours.
2.During operational hours, uphill access is restricted to the eastern edge of High Noon between the Base Area and Black Mountain Lodge. Access above Black Mountain Lodge is prohibited during operational hours.
3.You are considered a skier under the Colorado Skier Safety Act and should know “Your Responsibility Code”.
4.The mountain may be closed to uphill access when avalanche control, snowmaking, race training, or other special activities are taking place.
5.Uphill users are warned that snowmobiles, snowmaking equipment, snow grooming, winch cat cables and other equipment may be encountered at any time on the Mountain and you are responsible to stay clear of such equipment.
6.Entering closed terrain is prohibited. It is the user’s responsibility to know what is open or closed.
7.Terrain Parks are closed outside operational hours.
8.If the mountain is closed to uphill access, a closed sign will be posted at the bottom of High Noon trail in the base area. If you are unsure, please feel free to ask.
9.Dogs must be under control at all times. No dogs are allowed on the mountain during operating hours. Clean up after your dog.
10.Users accessing the mountain outside of normal operating hours do so at their own risk. Operational conditions may be variable including, but not limited to; closures removed for grooming operations, unfinished grooming activities, unmitigated avalanche hazards and limited visibility. Use extra caution!

I’m not Lou, but chiming in since I live in Europe:

I don’t know that European resorts have a “defined” policy. Every resort I know of in Europe allows uphill skiing without making much of a fuss about it. In fact, many of the alpine climbing huts are in the ranges behind/near ski areas. You can access these by taking the lift as many do, or by skinning up the whole area and then continuing your tour on the back side.

I just skied a short race this weekend at Flumserberg, Switzerland, and they actually light up the cat-tracks on Thursday, Friday, and Saturday nights so that people can train all season long. As is common, the restaurant/bar at the top stays open late (and busy) to feed folks and let them après ski after doing a couple of laps.

The ski-touring tradition is a lot older in Europe so this is pretty much common everywhere I have been in the Alps. Obviously, this explains why they pretty much dominate the world of ski mountaineering racing (like they do at soccer and Formula 1). However, humans are humans, and the vast majority of people skiing still alpine ski on piste. I would estimate that for every 1-2 folks touring, there are at least a hundred others purely down-hill skiing.

Hope that helps…