Although much archaeological work has been done in the San Pasqual Valley, all of it has been directed to San Pasqual Indian sites. Never has there been any formal archaeological work done in the valley directed at the Battle of San Pasqual. For a long time, it was the opinion of some archaeologists that any battlefield debris would have been long washed away due to the valley floor being also located in a flood plain. However, in 1994, two artifacts were discovered in the Park. The artifacts, a soldiers button and a piece of "grapeshot," were both found at just three inches.
Also found in 1994 was a identified flintlock lockscrew and a dropped musketball, consistent with others found at Mule Hill. This site is also consistent with where famous battle historian Colonel Berkley Lewis in 1970, found a center stock ram-rod holder or guide of a Brown Bess musket, the rifle commonly believed used by Mexican forces at the battle. No archaeological work related to the Battle of San Pasqual has ever been done in this area.
Also located within the five mile corridor is Mule Hill. Mule Hill is where a day after the Battle of San Pasqual, American forces were again attacked by Mexican forces, and pinned down in a defensive position for four nights and three days, until Marine and Navy reinforcements arrived. With the exception of a sweep conducted by archaeologists and historians, along with the assistance of Marine Corps mine sweepers in 1971, Mule Hill has never had any major archaeological dig done on it. This has attributed to over 250 pieces of artifact debris that have now been documented as being pilfered from the site by treasure hunters, much of which has been sold or traded into private collections. It should be noted that even the artifacts found in the 1971 sweep have disappeared at the Los Angeles County Museum of Natural History. Repeated attempts by the San Pasqual Battlefield Volunteer Association and others to get these artifacts returned to the San Pasqual Battlefield Museum has always met with negative results. The museum of Natural History has never been able to locate the documented artifacts.