There is one crosswalk for each area and year for decennial Census years 1990, 2000, 2010). Note that the Northern Mariana Islands are in the Guam file and the Virgin Islands are in the Puerto Rico file. There are no crosswalks for Puerto Rico, the Virgin Islands, Mariana Islands, Guam, or American Samoa for 1990.  For these areas, RSEI uses 2000 block boundaries and scales each cell's population by the overall ratio of 1990/2000 population for each area.

For Census year 2020, there are additional crosswalks from grid to block group, census tract, and ZIP code.

Field descriptions can be found in the RSEI Data Dictionary.
https://www.epa.gov/rsei/rsei-data-dictionary-census-crosswalks