Fort Worth to El Paso - not much near the interstate except at I-20 - Monahans Sandhills State Park and off I-10 - Davis Mountain State Park Or Balmorhea State Park. You could also work your way on state highways up to Carlsbad Caverns, New Mexico.
Then from Las Cruces, NM and I-10 west City of Rocks State Park is scenic which is north of Deming.
Continuing into Arizona on I-10 you'll find lots more. From Willcox you could tour Chiricahua Nat'l Monument with fantastic rock formations. At Benson you could do Tombstone and Bisbee and also Kartchner Caverns State Park has a nice campground and awesome cave tours. Lots to do in Tucson.
Once you hit I-8 at Casa Grande, AZ there's not much to the California state line at Yuma. From there you might as well head straight to San Diego.
Interstates aren't real exciting and we try to drive the secondary roads. Have a good trip!
Full-Timed for 16 Years
.... Back in S&B Again
Traveled 8 yr in a 40' 2004 Newmar Dutch Star Motorhome
& 8 yr in a 33' Travel Supreme 5th Wheel