Legal Question in Real Estate Law in California

First, "detrimental reliance" is an element of a cause of action for "promissory estoppel," not a cause of action in itself; i.e., a lawsuit would present a claim for promissory estoppel, not detrimental reliance. However, the cause of action (or lawsuit) only requires that there be an injustice that can only be rectified by enforcing the promise. Monetary harm per se is not necessary. Now, having said all that, I think promissory estoppel is not the best basis for a lawsuit here ..... I'd simply bring an action to enforce the oral contract. Promissory estoppel is useful in cases where the plaintiff can't assert the existence of a contract because he gave no consideration for the defendant's promise. Here' your oral agreement appears to have resulted from compromises made by both sides, Your compromises would be valid consideration, and it seems there is a valid oral contract. A question may arise as to whether the Statute of Frauds requires this contract to be in writing. I think it is an enforceable oral contract, in part because it doesn't transfer an interest in land, it only sets aside any dispute as to where the boundary was and is (but I'm not 100% certain about this part).