DocsTeach has long been one of my go-to recommendations for teachers of U.S. History. DocsTeach provides a wealth of digitized primary source artifacts that can be incorporated into lessons for elementary school, middle school, and high school students. You can search for those artifacts according to era in U.S. History, according to artifact type (text, photograph, map, audio, video), and you can search DocsTeach’s library according by keyword. Speaking of keyword search, if you search for “transcontinental railroad” you’ll find…