Mine is a 1995 (?) Nishiki Mountian Bike by RCD made in the USA. It's a diamond frame, unlike yours. I don't know the actual model because I covered the bike in "Police Line-Do Not Cross" tape only days after getting it (in '96). But it's a great bike. It has full Shimano STX, and a bunch of mods. Most notably, I replaced the horrible elastomer Rock Shox fork with a better model. The original fork bit the dust in one day of riding at Plattekill.

This bike is great for trail riding, but not so great for mountains. This design predates the Fisher Genesis geometry (of which I am a big fan) and so it is more closely related to a road bike than a MTB. It's a great urban assault vehicle. Very fast for something with fat tires.