Books Thru Bars San Diego is an extension of Groundwork Books; a leftist, non-herarchical, non-profit, workers' cooperative located at UCSD. They are 100% volunteer run, community based collective that has been sending books and resources to people incarcerated for years. Books Thru Bars San Diego strives to make literacy more accessible, as without access to the internet, books are one of the only places to turn for incarcerated people who wish to learn, imagine, study or grow.
Here is their official website in WordPress:
https://sdbooksthrubars.wordpress.com/