California Secretary of State occasional reports, History of California Initiatives (PDF files): lists all citizen-sponsored initiatives (even if withdrawn or failed to qualify), since 1912; includes vote percentages for approved measures and other summary statistical tables.
Prior versions (with generally the same types of information) are available in print (title varies) at the Law, Doe (main campus), or Institute of Governmental Studies (IGS) libraries: KFC708 .A87 1979 (Doe); 86 01929 (1985, IGS); KFC708 .E9 1988 (Doe) & 89 00049 (IGS); 90 01165 (1989, IGS); 94 00803 (1993, IGS); 96 00364 (1995 IGS); KFC708 .H57 1996 (Law) & 97 00176 (1996, IGS); KFC708 .H57 1998 (IGS); KFC708 .H57 2001 (IGS).
Recall History in California (Secretary of State) summarizes data from every recall attempt (statewide offices and Legislature) filed since 1913; tabulated from Complete List of Recall Attempts.
Despite a recent uptick in use of the referendum, the data can still be listed in less than five pages:
Statistics on measures that failed to qualify for the ballot (beyond the fact of failure itself) may be difficult or impossible to obtain. County election offices (responsible for determining if enough petition signatures were collected) are obligated to preserve the petitions only until 8 months after the certification of results from the election. The county thereafter may destroy the records unless a lawsuit or governmental investigation is pending. See Cal. Elec. Code § 17200. Once petitions are filed with county officials, they are generally not considered public records for purposes of Public Records Act requests. See Cal. Gov't Code § 6253.5.