Are the needles usually held singly?
CLUE: the tree is native in scattered areas from southern Idaho to Mexico.
It is a singleleaf pinyon.
- OR -
Are the needles mostly clustered in groups of 2 (occasionally 1's or 3's)?
CLUE: the tree is native throughout parts of the Southwest.
It is a pinyon (Colorado pinyon).
- OR -
Are the needles mostly clustered in groups of 4?
CLUE: the tree is native only to the mountains of southern California.
It is a Parry pinyon.