as our old RV (and us) don't like crossing mountains... what is the lowest altitude going from the west coast to the east coast across the mountains. i was told that I10 is flat but elpaso is 4000 f...
I-10 in New Mexico at Lordsburg near the border of Arizona is 4250 elevation. I-10 in Arizona at Wilcox (the highest in Arizona on I-10) is 4259 elevation. I-10 at Tucson, west of Wilcox is 2643 elevation.
As you can see, the elevation 'climbs' on I-10 in Arizona are mild and very easy to drive.