I have a 1990. My pressure reads on the high side until the car warms a bit. The gauge looks scarier the colder the weather is.
[SIGPIC][/SIGPIC]
Just recently came aboard to the site. Most of my miata-related internet trolling is on CR.net.
Edit: ^^ Was a reply to jeff_man.
Just out of curiosity, did you happen to change the oil/filter shortly before this incident? Most filters have a pressure relief valve in them, and some of the cheaper filters don't always perform adequatley. Just a shot in the dark.