Simplify the following text for a Grade 10 native English-speaking person.
Original: In the fall of 1917 , McCarroll was driving on the road leading to her office near Indio , California on a stretch of highway that would later be incorporated into U.S. Route 99 .
Simplified: In the fall of 1917 , McCarroll was driving on the road leading to her office near Indio , California on a stretch of highway that would later become part of U.S. Route 99 .