Somebody leaving Castle Air Force Base would also have joined Highway 99 (just like Kathleen Johns) and headed 34 miles to Modesto and then took Highway 132. Bearing in mind Kathleen Johns described her abductor as a "clean shaven and very neatly dressed man, thinking he may have been a service man or something", the possibility he had left one of these military airfields in his wing walker boots or some other military footwear, is certainly worthy of considerarion. When he had convinced Kathleen to take a ride with him, she noted that the "stranger's shoes had been shined so brightly, 'spit-shined' that they reflected the yellow interior lights of the car". The most direct route from both of these military airfields drops right onto Highway 132 and the route that Kathleen Johns noticed she had picked up a tail that night. The map below shows the position where Kathleen Johns vehicle was discovered burnt out, and the exact location where somebody traveling from NASA Crows Landing would have picked up Highway 132.
Castle Air Force Base (1941–1995) is a former United States Air Force Strategic Air Command base located northeast of Atwater, northwest of Merced and about 115 miles south of Sacramento, California. The base, located in unincorporated Merced County, was closed in 1995 pursuant to a Base Realignment and Closure Commission decision following the end of the Cold War and the disestablishment of Strategic Air Command. It is now known as the Castle Airport Aviation and Development Center. From April 1968 to April 1974, the 93rd operated a special B-52 replacement training unit to support SAC's B-52 operation in Southeast Asia. Also, the 328th and 329th Bomb Squadrons deployed to U-Tapao Royal Thai Navy Airfield, Thailand where they flew combat missions over Vietnam, Cambodia, and Laos during the Vietnam War. link.
Crows Landing was an auxiliary airfield connected to Alameda Naval Air Station and Moffett Federal Airfield in Santa Clara County, both in the Bay Area where we know the Zodiac Killer operated. Did these military bases play any part in the Zodiac Killer's chosen profession, being contracted to work between the Patterson area, just south of Modesto, and the eastern fringe of San Francisco? This area of work would certainly facilitate his mailing of letters without too much deviation.