Not sure if it's manzanita, but it looks like hardwood and it looks dry enough to be safe. I've used a lot of dried out hardwood that I've picked up, but I always knew without doubt what kind it was. Most hardwoods are safe to use in aquariums except fragrant types, such as apples and other fruits and things like lilac bushes. These become safe with time, but it takes a lot longer than something like cottonwood or manzanita. I'd make sure it's completely dry and I'd boil it first. The biggest thing I'd be worried about is that it may have been exposed to any kind of chemical and that those chemicals were absorbed into the wood, especially pesticides and herbicides. Even boiling probably won't help with that.
WYite