Cal. Probate Code § 16347

(a) If a fiduciary determines that an allocation between income and principal required by Section 16348, 16349, 16350, 16351, or 16354 is insubstantial, the fiduciary may allocate the entire amount to principal, unless subdivision (e) of Section 16327 applies to the allocation. (b) A fiduciary may presume an allocation is insubstantial under subdivision (a) if both of the following conditions are met: (1) The amount of the allocation would increase or decrease net income in an accounting period, as determined before the allocation, by less than 10 percent. (2) The asset producing the receipt to be allocated has a fair market value of less than 10 percent of the total fair market value of the assets owned or held by the fiduciary at the beginning of the accounting period. (c) The power to make a determination under subdivision (a) may be either of the following: (1) Exercised by a cofiduciary in the manner described in subdivision (f) of Section 16327. (2) Released or delegated for a reason described in subdivision (g) of Section 16327, and in the manner described in subdivision (h) of Section 16327. (d) This section does not impose a duty on the trustee to make an allocation under this section, and the trustee is not liable for failure to make an allocation under this section.