help me find a book i read in middle school. i can't remember the title.?

for a few years now, i’ve been thinking about this great book i read years ago. i don’t remember the title, author, or much about the story. i just remember i really liked it and don’t think i finished it. i’ll try to describe the book as best as i can. i remember in either the front or the back of the book is a map. the story begins with the girl going to her grandma’s house for the summer i believe. there’s a mysterious mountain or raised up lake in the little city her grandma lived. i know it says in the book that people don’t go up the mountain because at the top is fog or clouds and nobody knows what’s in it. planes can’t see what’s inside either, and i think it said something about when planes or helicopters go over it, the instruments go funny. anyways, the girl finds a map and a staff? in her grandma’s house and goes up the mountain. then something about her hiding in a tree because she’s being chased by someone and something with the staff hitting the tree and she ends up going back in time. she meets indians? and learns their way. and this part i’m confused by, i don’t know if i got another book mixed up with it but i think in the end, she gets dragged underwater by alien things and talks to these things underwater? i’m not sure about that part. anyways, i don’t think i finished it and it would be great if anyone could help me find it.
it’s a sci fi teens book i’m guessing. whenever she’s hiding in the tree a powerful storm comes along and there’s thunder and lightning and that’s what knocks her out and when she wakes up she’s inside the mountain/valley thing.