Your own front yard, or back yard, or the street, of course, preferably with illegal fireworks. Or the beach. As a friend put it, for any holiday celebrating the overthrow of the government, the question of whether your fireworks are legal simply shouldn't come up.
Most of California's way too dry to allow the things, but there's one town near San Francisco (Pacifica) that's always wet enough they're not worried about moderate levels of fireworks, so the local fire department sells them, and you're allowed to set them off down on the beach, and in practice locals also set them off on the street. Several friends have lived there, and we've had a few good July 4th parties and a Canada Day party (too foggy, but lots of fun; it's July 1, and it was the weekend that year.)
My town used to have a freeway exit that was closed for construction, so there was a big pile of dirt twice as high as the bridge is now, and the neighbors would all take our lawn chairs up to the top to watch fireworks, including the official town shindig (minus the traffic), and the amusement park down the road, a couple of towns north and south, and the illegal backyard fireworks. Another place I lived was on a bay, and for some big firework years we could go down to the dock and see fireworks from a bunch of different towns across the water.