Happens not infrequently during winter months. See thread here.

Have they rebooked you on a new connection to SFO? If not, you should call and see if you can get it rebooked now. Check the available flights first and have your best alternative(s) in mind.

Whether UA will give you any compensation probably depends on how substantial the delay in getting you to SFO. If it's only two hours, not really worth complaining about IMO.