This study presents the latest progresses on seismic imaging and monitoring of three volcanos of various size and tectonic settings in the western U.S., i.e., Yellowstone, Long Valley caldera and Mount St. Helens. High-resolution 3D crustal shear-wave (Vs) structures were constructed using seismic ambient noise, which are mainly resulted from wave action in the global oceans. A particular innovation of this study is the incorporation of multi-component seismic data to constrain the anisotropic properties of the magmatic reservoirs beneath the volcanos. Pronounced low velocities regions are found to be coincident with strong positive anisotropy beneath all three volcanic systems and are interpreted to be magmatic reservoirs with fine-scale layering. Such layering structures may represent sill-type intrusions of molten melts, and their existence demonstrates that magmatic reservoirs beneath these volcanoes can grow incrementally from the deep through a long-term process. The similarity of magma reservoir anisotropy in varied tectonic settings suggests that such mid-crustal sill complexes may be ubiquitous features of large magmatic systems, and that anisotropy should be considered to seismically estimate melt content and mobility. In this talk, I will also share results from ongoing research to show how additional seismic monitoring using 10-year seismic noise data provide further insights for the evolving state of the Long Valley caldera.