The first two images below are samples from a book which appears to be a record of payments in kind made to soldiers in the San Francisco Presidio in 1817, which perhaps confirms the suggestion in the question that they were unpaid during the war.


The document in the following images appears to show the payments made to the officers and men in the San Francisco Presidio for the period 1 January 1828 to 31 March 1828. This is of course outside the period of Spanish rule but I believe the Presidio was still manned by the same personnel as before Mexican independence in 1821.


The above documents form part of the Vallejo Family Papers collection reference BANC MSS C-B 441 at The Bancroft Library, University of California, Berkeley.