The marsh is fed by the upwelling of a perched water table dammed by the Nogales Formation; a bedrock of sedimentary conglomerate. When the Anza expedition camped here on October 14, 1775, it probably was a sedge marsh. The normal progression of plant establishment is lichens, mosses, sedges, cattails, and trees in a marsh type ecosystem. Las Lagunas is considered one of the last remaining fresh water marshes on the upper Santa Cruz River Basin.
The marsh has been improved over the years by the elimination (by hand) of some cattail creating open water needed for waterfowl. Control of cattails is accomplished by U.S. Fish and Wildlife Service approved aquatic herbicide. The riparian bank includes a gallery of Cottonwood and Willow trees bordering the edge of the wetlands along the south road side. Opposite on the north side of the wetlands is a grove of Arundo, a non-native giant reed originally brought by the Spaniards. Although the Arundo is considered by some to be an invasive plant, we maintain and monitor it as it has the benefit of providing a natural barrier from the parking lot of the neighboring warehouse. Aquatic life includes mosquito fish, and non-native bullfrogs and crayfish. Water testing revealed low dissolved oxygen levels, and no significant E-coli input. Hundreds of birds and waterfowl make their home here or rest during migration.