This car, shown at the rainy March 23, 1958 SCCA race event at Stockton airport in Northern California Stockton, has earned full-scale "Mystery Car" status. 

Stu "Dr. Etceterini" Schaller, an expert on small-bore Italian sports/racers, identified the car as a Cisitalia.  A look at the Cisitalia website (Entrar-Galeria- Pasado-2-6) shows the "Cisitalia 202 SMM Spyder Nuvolari".  The details of that car and this one match up, except for one thing -- that pesky Maserati trident in this car's grille!

Here's more from Stu "Dr. Etceterini" Schaller on this car:

"I think the car might even be one particular car, called the Razzo, rather than a "standard" Nuvolari spider.   If you look close, you can see kind of wings at the top of the front wheel arches, and as far as I am aware, the Razzo was the only Cisitalia spider that had them.   The Razzo also had cut down doors, but it is impossible to see if the car has them in the photos shown.   Regardless, I am 100% certain that it is a Cisitalia; you can even see the Cisitalia badge between on the top of the nose of the car, in front of the hood.   The standard motor would have been 1100cc, but it is certainly possible a 1500 or 2 liter Maserati A6 motor could have been put in the car."

Did  someone actually transplant a rare, fragile, expensive and exotic Maserati A6GCS engine into a super-exotic one-off Cisitalia Spyder?

Stu & I started a discussion of this car on the Atlas F1 "Nostalgia Forum".