Floods were expected. Dams and levees had been built and rebuilt at the mouth of arroyos and along the Rio since Pueblo times. The 1885 levee was built after a huge flood in 1884 and had already been breached twice before a night in September 1903 when a 19,000 cfs flow broke through a dike and wiped out the modest town of Alameda.
The water wasn't just from the river. Extensive grazing of the lands on the mesa east of the valley contributed to increasing sediment loss. Waters swept up hunks of dirt and trees along the banks in thick powerful rushing mud that spilled into the valley.
Any hope that nature wouldn't repeat the insult before the levee was rebuilt again was dashed the following year when another flood, almost as large, overwhelmed the valley again. After this one nearly all the structures, including two parish churches and three villages, had been destroyed. Many residents moved to higher land along the valley edges. Or moved to California.
Into this scene of community disorder quietly stepped a prominent attorney named Alonzo B. McMillen. And while remaining residents of the Alameda grant were rebuilding their lives, acequias, homes and churches, McMillen filed for court partition of the Alameda grant on behalf of one Vincenta Montoya, heir of Vigil, late of California. Within five years, McMillen owned 45% of the grant. And by 1920 his San Mateo Land Company owned an estimated 75,000 acres of the former 89,000 acre Alameda Land Grant. This is where Rio Rancho is today.