It is a bit of a frankenbike - been repainted and rebadged. Not 100% sure it is a pine mountain either despite what the stickers say. U brake mounted on the BB shell would be 88 possibly 89. 90 onwards were all cantis. Zolatone 90 was light grey, 91 dark grey. Those look to be 91 decals. Stem is a bit too pointy up in the sky to be 90 or 91 pine mountain, but it is a Marin stem. Rear stays aren't 90 or 91 stays - those are tapered, 90/91 were 'afterburners' and constant diameter for their full length.