Up In The Sky, What Was That?

About 14:40 today, while driving on S Los Carneros next to the airport, I (and some of my fellow drivers) were overflown by what looked like a delta-winged single engine aircraft. It looked (and sounded) like a fighter plane, however I do not believe the US military uses any delta-winged aircraft. Does anyone know the make/model of this plane and who might have been flying it? It was an awesome experience and would love to know more.