We request salary support for Prof. Craig Jones from the University of Colorado, Boulder to spend three months at the University of Luxembourg for the period May-July, 2015 working with Profs. Francis and van Dam. The aim of the visit is to investigate using absolute gravity to improve our understanding of the tectonic history of the Sierra Nevada mountain range in California. The team of Jones, van Dam, and Francis propose to use absolute gravity (AG) to constrain the geometry of present day uplift in the range and thereby constrain the mechanisms contributing to the uplift.There are two primary goals that we want to accomplish during the visit. First, we want to see if absolute gravity observations can be used to constrain the actual uplift rate and also the differences between presently advocated models for uplift. This goal requires Jones to identify the portions of the Sierra where differences are most critical and Francis and van Dam to define the characteristics necessary to make a useful and robust series of measurements with the AG meter. The team will then model the different tectonic mechanisms describing the evolution of the Sierra Nevada to predict the three-dimensional surface displacements, i.e. what would GPS observe, and absolute gravity changes for the different mechanisms. The modelling will entail adapting software already written by Francis and van Dam. However, we will engage in discussions with Dr. A. Zilian and Dr. Bordas, specialists in finite element and material modelling at the University of Luxembourg, to explore the possibility of incorporating innovative techniques or ideas into our models.The second goal of this request will be to write a proposal to actually carry out the fieldwork. The results of modeling work described above will be necessary to justify the proposed request for funding the fieldwork. A precise and thorough cost breakdown will also be required. Jones’s experience in the Sierra Nevada and van Dam and Francis’s experience in Yellowstone will contribute to developing a realistic budget. The proposal will be submitted to the Solid Earth Panel of the National Science Foundation (USA) and perhaps to the Fond National de la Recherche (depending on how the FNR program evolves in the near future). The modelling and, to a lesser extent the proposal writing, will benefit by having all the scientists in the same place working together on a day-to-day basis. The team will need to refer to maps and to develop realistic surface displacement models, tasks that will proceed much more quickly and smoothly by having the team in the same location and in the same time zone.As a cost benefit, Jones will travel with his wife, Prof. Anne Sheehan (http://cires.colorado.edu/science/groups/sheehan/), a geophysicist with expertise in tectonics and seismology. Sheehan already has salary support from an award from the University of Colorado. van Dam and Sheehan are currently collaborating on a project in the Rio Grande Rift and will begin a collaboration on an analysis of the seismic data from Greenland.Jones and his wife will give seismology and tectonics lectures to the Geophysical Laboratory (GL) and any other interested parties. Jones and Sheehan will also work with R. Deplaen, a Phd Student in the GL to use seismology to investigate the shallow velocity structure beneath the Kawah Ijen Volcano in Indonesia, and with Prof. N. Teferle who has established a continuously operating GPS station on South Georgia Island to unravel the tectonic history of the Scotia Plate.