Dan L. Mosier has over 35 years of experience as a geologist (BA, SFSU; MS, CSUH) and over 50 years of experience as a historical researcher. He is author or coauthor of over 75 scientific papers on geology, which include Relationship of grade, tonnage, and basement lithology in volcanic-hosted epithermal precious- and base-metal quartz-adularia-type districts; Podiform chromite deposits—Database and grade and tonnage models; Volcanogenic massive sulfide deposit density; and Tertiary volcanic history of the Markleeville Peak area, Alpine County, California. 

In history and genealogy, he has published over 660 articles and 9 books, which include History of Tesla – A California Coal Mining Town; with his wife Page, Alameda County Place Names; Brick making in the Livermore Valley; and San Francisco City Hall Bricks. He created the once popular California Geneaology Index website and cofounded the Norcal Genealogy Index website, for which he wrote many articles.

In 1970, Mosier began collecting and researching marked bricks. In 1990, while studying the bricks of the Carnegie Brick and Pottery Company, in San Joaquin County, California, he began the study of documenting and identifying bricks for the purpose of assigning them to brickyards. His method of using mineralogy, petrology, history, and archaeology has been successful in identifying the makers of bricks.

In 2001, Mosier launched the California Bricks website to publish his brick research and articles and to help archaeologists identify bricks from California. He has maintained a database and archives on over 3,000 California bricks. In 2018, he developed an app using his brick identification method that can successfully identify the maker of a brick for the San Francisco region. In 2017, he launched the Washington Bricks website. 

In 1995, Mosier was awarded the Superior Service Award by the U. S. Department of Interior for his geologic research work at the U. S. Geological Survey. In 2011, he was nominated for the Crabtree Award for outstanding advocational archaeologist by the Society for American Archaeology. In 2013, he was awarded the Mark Raymond Harrington Award for archaeological conservation by the Society for California Archaeology.