Summary: Ejecta associated with the Xalapasco de la Joya maar 33 km northeast of San Luis Potosi, SLP, Mexico, contain a diverse assemblage of nodules of postulated lower-crust/upper-mantle origin. Spinel lherzolites constitute the most abundant group of nodules and display chemical evidence that crystallization or equilibration took place at temperatures and pressures consistent with upper mantle genesis. Estimated equilibration temperatures and pressures range from 825 to 1025 °C and 7 to 19 kb.