Let us assume the following facts:
- Alice places a container, log, and some item(s) at some place, publicizes its location and invites others to come and swap objects
- Bob comes, takes the item(s) present in the container and leaves some other item(s) in exchange.
- Carol comes after Bob, takes "everything" (see below) and leaves nothing.
- The police somehow finds out irrefutable proof of all the above, and decides to charge Carol for theft.
Easy case #1: Carol does not know what she is doing
Carol is the farmer on whose land the geocache was placed. She has no interest in or knowledge of geocaching. She removes the container and discards it. (Alternatively, Carol is an eco-friendly hiker, and wants to clean up garbage left by unethical hikers.)
Carol(’s lawyer) will argue that under ORS 164.035 (1)(b) she reasonably believed she "had a right to acquire or dispose of it as [she] did". It seems likely to succeed.
Such a defense would of course be less likely to work depending on certain circumstances - for example, it becomes untenable if the prosecution can show that Alice has an active account on geocaching sites.
Easy case #2: Carol knows geocaching, and she takes the box
My understanding after reading the geocaching.com policies is that whoever places a container is responsible for their maintenance, and if necessary removal. There is therefore little doubt that this person is and remains the owner of the container (and possibly the log), and that anyone familiar with geocaching should be aware of it.
Therefore, Carol took some property with full knowledge that she deprived the legitimate owner from it. She is guilty of the theft of the box at least (under 164.015). The exact status of its content does not matter much for criminal purposes of establishing guilt. (It might or might not be relevant to sentencing.)
Interesting case: Carol knows geocaching, takes the items and leaves the box
I am not a practitioner of US law (let alone Oregon law), and therefore what follows is highly speculative. I think the prosecution can successfully argue that Carol stole the items.
Carol can try to rely on either prong of ORS 164.035 (1).
Prong (b) seems likely to fail. If Carol is aware of geocaching basics, she knows that the social expectation is to replace the items one takes. There might be some debate about what a proper replacement could be, but "nothing" does not fit the bill.
Prong (a) is where Carol argues that the items were abandoned (without owner) and therefore ripe for taking by anyone. The prosecution will try to argue that they were not. I think they have the better side of the argument, (but see above: not an Oregon law practitioner).
I can see two possible arguments from the prosecution:
- the items were Bob’s all along
- it is not clear who the items belong to, but the circumstances in which Carol took them are not reasonable
Option 1 relies on the similarity with a shop. Shoppers can physically pick up goods, but the goods belong to the shop until money changes hand at the checkout. The fact that the shop left the items easily accessible to shoppers does not establish the shop’s intention of abandoning them; if one takes items out of the shop with the intention not to pay, that is theft.
In that theory, Bob, by leaving his items in the geocache, is offering a contract of "I give you my items, you give yours to someone else". (Bob accepted a similar contract from Alice.) Carol might refuse to accept that contract, but she has no right to take Bob’s items without compensation. The contract might be vague (how does "equal or higher value" apply exactly?), but there is no doubt that Carol, by leaving nothing, did not follow its terms.
The defense would likely argue that a shop keeps precautions to avoid shoplifting, that unsold products are taken back in storage or disposed of by the owner, etc. - that is, a shop exercises more control over the items than Bob does.
Option 2 would be to say that Bob left Alice, the maintainer of the geocache, in charge of handling the items he left. It might be that Bob kept title to the items, or it might be that he transferred that title to Alice. At any rate, the rest of the story is similar to option 1: Alice (instead of Bob) offers a contract to Carol ("take something from my box, leave something else, and I promise I will let others do the same thing for a reasonable period of time"), Carol refuses and steals the items instead.
A hypothetical would be if Carol walked to the lost&found counter at a train station, and claimed falsely that she had lost a green bag. If Alice (the train station clerk) had found a green bag sooner in the day, and delivered it to Carol, Carol would be guilty of theft; even if nobody really knows whose bag it was, it was certainly someone’s, and not Carol’s.
The defense would likely argue that a mislaid bag is significantly different. The owner of a mislaid bag presumably wants it to be returned (Carol should take reasonable steps so that it happens per 164.065). On the other hand, Bob does not want the items to be returned to him, therefore they are not mislaid (and it does not matter that he wants something else to happen to them).