Welcome to the RTA Forum!

Where in Texas are you starting from and where in California are you heading?

I'd say for the most part it will make a lot more sense to drive to Phoenix via I-10 and then head north to Flagstaff and the Grand Canyon before continuing west towards CA on I-40.

4 days should likely be enough time to make the trip, but again depending upon your exact starting and stopping points, it could be rushed to fit in a trip to the Canyon.