The reason there is a mound at Pueblo Grande is erosion. Mud from upper story roofs and walls have been eroding away for hundreds of years. Water, wind, and vibrations have been at work to weaken the mound so that, given time, the mound would continue to erode away, lower and lower, until it was merely a bump on the ground. At least they would if efforts were not set in place to preserve the mound as we know it today.
The National Park Service, the City Archaeologist and PGM maintenance staff began stabilization efforts around 1990 to mitigate the effects of vibrations and rainfall. Rock and dirt fill has been placed into the excavated portions of the mounds with the exception of the room at the southwest corner. Dirt has been placed up against the sides of the outer walls, offering support. Mudslinging volunteers come out once a month during the nicer months of the year and re-plaster walls, so erosion damages new mud before it can affect original walls. Trees and shrubs are not allowed on the mound as the roots could cause serious structural damage.
Drains have been installed along the trail on the mound and in specific areas where water was observed to be pooling and causing erosion. The drains were carefully placed in a way that they would not impact the mound itself, but that they would effectively carry water away to where it would not damage the mound structure.
One other cause of erosion and damage is from burrowing creatures such as squirrels or ground squirrels. As much as we love to see these animals while we are out and about, we do need to keep their numbers under control. There are occasions where we will trap these little critters and relocate them to an area where they will not be able to do harm to any archaeology.
We will cover the more about the mudslingers, their support efforts and mound preservation in a later posting. If you would like to be a part of this fun and helpful group, contact the museum for more information on volunteering.
Posted by Dan Gronseth - Park Ranger II