Final answer:
The internal control procedure that involves maintaining an adequate audit trail is the maintenance of accounting records. This ensures financial transactions are traceable and verifiable for accuracy and integrity.
Step-by-step explanation:
An accounting system that maintains an adequate audit trail is implementing the internal control procedure of accounting records. This involves keeping detailed records of all financial transactions that could be reviewed at a later date for verification purposes. It allows organizations to trace each transaction from its inception through to its completion and provides a clear path for auditors to follow, ensuring the accuracy and integrity of financial data.