Legal Question in Securities Law in California

I could not find any corporation of that name registered with the California Secretary of State, although there are 53 companies (both active and defunct) with "United Properties" in the name. You might take them to a stockbroker; they have the means to look up the securities of obscure companies to see whether they have value or are only interesting collectors' items. The company may have gone out of business long ago (when are the bonds dated?) or merged into another company. A securities brokerage should be able to assist.