Large ignimbrite eruptions pose great hazards to society, including ashfall and pyroclastic density currents, and they affect global climate. This thesis provides insight into their crustal magma architecture, the difference between zoned versus unzoned magmas, and the timescales and fluxes of magma reservoir construction using petrology, zircon geochronology, thermal modelling, zircon modelling, and data clustering. This thesis focused on four large ignimbrites in Colorado, USA: the 150 km3 zoned Rat Creek Tuff, 250 km3 dacitic Cebolla Creek Tuff, 500 km3 zoned Nelson Mountain Tuff, and 500 km3 dacitic Snowshoe Mountain Tuff, from oldest to youngest, erupted at approximately 27 Ma. Magma reservoirs extend from 470 MPa to 110 MPa and were built over millions of years at relatively low-flux magma input. Unzoned ignimbrites have a deeper crystallization signature than zoned ignimbrites. Additionally, data clustering provides a rapid, robust, and objective method of uniquely fingerprinting ignimbrites, having far-reaching implications for tephrochronology.