Traveling Sunday

[Byzantine]

We're driving and don't know where we'll be Sunday. We're trying to get from California to PA by Wednesday (it's Friday night here). How much do we need to plan where we'll stay around whether there's a church? Like, if we could put on an extra 100 miles but wouldn't be able to get to church on Sunday because of it...? Thanks!

[cappie]

The Sunday obligation is one of the Precepts of the Church, duties that the Catholic Church requires of all the faithful. These aren't mere guidelines, but rather a list of things that the Church teaches are necessary for Christians to do in order to live the Christian life. For that reason, they are binding under pain of mortal sin, so it's important not to disregard them for anything less than serious reasons.
The Catechism of the Catholic Church states that the first precept is "You shall attend Mass on Sundays and holy days of obligation and rest from servile labor." You'll notice that the statement isn't qualified; it does not say, "When you are at home" or "When you're no more than X miles away from your home parish." Our obligation is binding on every Sunday and Holy Day of Obligation, no matter where we are.
That said, we may find ourselves in circumstances in which we are unable to fulfill our Sunday obligation, and you have suggested one. Of course, if we find ourselves on Sunday morning in a town with which we're unfamiliar, we should do our best to locate a Catholic church and to attend Mass. But if, through no fault of our own, we discover that there is no church, or that we're unable to attend Mass at the scheduled time (for a good reason, and not, say, simply because we want to go swimming), then we haven't deliberately violated the precept of the Church.