Cal. Code Regs. tit. 8, § 6279 – Falling Cuts.

(a) Undercuts shall be of a size to guide the trees in the intended direction and minimize the possibility of splitting.
(b) In trees of sound wood and no perceptible lean, the undercut shall be no less than ¼ the diameter of the tree and the face opening shall be no less than ¹/₅ the diameter of the tree.
(c) The backcut shall always be started at or above the level of the horizontal cut of the undercut.
(d) Trees shall not be left standing after the undercut is made under normal conditions.

Note: Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code.