Ground penetrating radar (GPR), thermal infrared imagery (TIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) provide an understanding of shallow subsurface altered zones in the Old Faithful Geyser area. The GPR and TIR are temporal snapshots of the hydrothermal system; GPR reflections suggest extensive subsurface zones of hydrothermal alteration. SEM-XRD document changes in hydrologic conditions. SEM-XRD analyses of sinters demonstrate a multi-stage formation history, pH-temperature hydrodynamic changes, and dissolution by acidic steam condensate. TIR images show surface thermal trends that are consistent with mapped fractures and/or faults and with the GPR, SEM and XRD results. (C) 2017 Elsevier Ltd. All rights reserved.