The USGS Crustal Geophysics and Geochemistry Science Center (CGGSC) collaborated with the USGS Data at Risk (DaR) team to preserve and release a subset of magnetotelluric data from the San Andreas Fault in Parkfield, California. The San Andreas Fault data were collected by the Branch of Geophysics, a precursor to the now CGGSC, between 1989 and 1994. The magnetotelluric data selected for this preservation project were collected in 1990 using USGS portable truck mounted systems that measure the distribution of electrical conductivity beneath the surface of the earth. Truck mounted systems of this era outputted data to 3.5 inch discs, from which data were recovered and transformed to binary or ASCII formats using proprietary software. This USGS software release is a set of Python-based scripts developed by the DaR team to convert time-series and cross-powers ASCII formatted magnetelluric data files to EDI format, a common modern format for magnetotelluric modelling. While this code was designed for the 1990 Parkfield, California dataset, it can be generalized to batch process other magnetotelluric data collections.