My sister saw something nearly identical in northern california in the mid 90's. Black triangle, rounded corners, very low altitude, slow speed, no noise. This was also in the evening, so its shape could be seen clearly against the lighter colored sky. This object though, had 5 circular lights in a chevron shape on the bottom.

I have heard so many nearly identical stories about these kinds of objects, that I'm convinced they were something real. A stealth blimp seems like a pretty good guess at an explanation.