Stevens Pass does not have a dedicated tubing or sledding area. You should go to Summit at Snoqualmie.
It is not suitable for sledding, it is a business catering to downhill skiing and snowboarding.
I have not seen anyone to use sleds as everyone was doing ski but I am sure you can use sleds and no one will stop you and you will get lots of space to use sleds. It will be better if you check on their website about site seeing availability so that you can go up the mountain also
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