[3] In October 1851, he ran against Whig Party candidate, Tod Robinson, to fill the seat of Serranus Clinton Hastings, and won a six year term.

[3] Heydenfeldt's notable opinions include Irwin v. Phillips,[5] which established the doctrine of prior appropriation in western water law jurisprudence.

[9] While in private practice, Heydenfeldt argued before the California Supreme Court in Ex Parte Newman (1858),[10] where he successfully defended a Jewish man's right to work on Sunday.

[11] In 1862, during the Civil War, he refused on principle to take a test oath for lawyers of loyalty to the Union cause (as did Virginia-born James D. Thornton), which led to his semi-retirement from the Bar.

[12] His son, Solomon, graduated from Santa Clara University and in October 1872 became an attorney, and his nephew, Walter P. Levy, was a judge of the San Francisco Superior Court.