Does this book sound familiar?

I vaguely recall reading a book as a young pre-teen that I really enjoyed. I cannot remember much about it. I recall it involved a kid moving to the country or into the hills or something. There was some mystery involved. The only details I can recall is that there was supposed to be some creek in the area with no bottom, so he tied a string around a rock to try to find the bottom and couldn't. I also vaguely recall him hunting for sapphires and rubbies in the hills by looking under groups of weeds. I know that isn't much, but maybe it will sound familiar to you. Any assistance would be great!!