Check your local law. In Washington, the chapter RCW 63.21 says what you are supposed to do. The first part of the law has apparently been satisfieds:
Any person who finds property that is not unlawful to possess, the
owner of which is unknown, and who wishes to claim the found property
Then you need to get a signed appraisal stating current market value from a qualified person engaged in buying or selling the items, or by a district court judge (I have no idea where district court judges get their qualifications to appraise bricks), then within 7 days, report this to the cief LEO where the stuff was found (and surrender it, if requested). You also have to serve written notice upon that officer stating your to claim the property. The burden now shifts to the government, which must publish notices in a local newspaper at least weakly, for 2 weeks. The notice might be publishable in a no-cost venue, in case the publication cost is greater than the value of the stuff. If the owner appears and establishes ownership, that's the end of the finder's potential interest. If the owner does not show up, the property will be released to the finder once he has paid the government's publishing expenses plus $10, but if the goods are appraised at less than publishing cost, there is no fee. As a finder, you have 30 days after that 60 days to pay required costs, otherwise it goes to the government. There are some exceptions, things not subject to finders-keepers (crab pots, secured vessels, motor vehicles, unclaimed property in the hands of a bailee).
If you do not comply with these requirements, you forfeit any right to the property and you are liable to the property owner for the value of the bricks.
Under the definition of theft, you have a defense that
The property or service was appropriated openly and avowedly under a
claim of title made in good faith, even though the claim be untenable
since you presumably intend to claim ownership of the bricks under the lost property statute.