Just about all evidence of the old Marquardt Aviation Co. plant along the west side of Van Nuys Airport has been removed. Started by Caltech graduate Roy Marquardt, the company moved to the Valley in the late 1940s and became a major defense contractor, specializing in ramjet engines. There's now a gleaming new industrial park in its place. A website history of Marquardt is here, and there are some photos of the old plant here.