I 35 s I 90 w 75 s to Sioux City 20 w 81 s 30 w in Grand Island, NE I 80 west Those roads are all good roads and will save you some time... Your best way is to work your way to I 80 then I 80 all the way to California. I 90 is a lot more hills, and some big hills at that. You will have a big down grade just as you get to Salt Lake on I 80 and a big pull and down grade at Truckee, Ca on I 80 over Donner Summit. You will have a few other hills but those 2 are the biggest.