hey blacktail,
I've harvested yew in Oregon and it's not just high elevation that makes yew have tight growth rings. I've cut yew on the east side of the cascades, just west of Sisters. And even though the yew was at very low elevation (in the foothills of the mountains) it had very tight rings. And that is also because it grows on the dry side of the mountains, where rainfall is much less.
I don't worry much about high elevation or low elevation when looking for yew. What I look for is straight, knot free staves, regardless of where the yew grows. I've seen tons of yew trees that were high in the Cascades that were useless for bows because they were just about covered in branches, whereas some lower elevation yew was much cleaner and was much better suited for bows.
So there are a lot of other factors that play into the quality of yew besides just elevation alone. But I wouldn't worry much about it. If it's clean and straight and you can see a bow in it, then take it. But if you want a REALLY good bow wood, go out into the desert and cut some juniper. That stuff is amazing when sinew backed....it's super flexible and can be snappy as hell. I call it "desert yew", and I think it makes the best sinew backed bow there is. Yew can't hold a candle to it in my opinion.....
