ABANDONED. Kid finds some sort of creature in a crevice in the cliff in his backyard

[Melanie Linn]

I remember reading it sometime in the 90s, so probably was a teen/young adult book. In it, there was a sort of dejected kid who was on his own a lot and found this creature (maybe an abused cat?) in an opening in a cliff (rocks?) in his backyard.

[Tab]

Was this a fantasy, science fiction, comedy, etc?
Anything about the cover?

[Lobstergirl, au gratin]

Melanie Linn left the group. Moving to Abandoned.