California's tracing doctrine did not arrive complete. Courts built it case by case across eight decades, reasoning from raw principles when no established method existed. The 1960s brought structural consistency; the 1970s produced the presumption framework that permanently redefined how disputed assets are characterized. The early 1980s then pressed those rules against appreciation claims, reimbursement disputes, and asset types the founding courts never anticipated. Twenty-seven cases, four eras, the complete foundation every California tracing analysis still rests on.