California Underground Online Exhibits - An overview of the formation of caves, cave conservation, photography and wildlife together with local educational resources. Diagrams, pictures and slide shows.
Cavechat.org - NSS discussion forum for US cavers including sections for cave diving, news, conservation, equipment, photography, rescue and surveying.
Caving From Spadout - Articles on the terminology, techniques and gear used for caving. Discussion boards, editable information, feedback and links.
- A wide-ranging introduction to the geology of caves. Organised by geological feature with pictures and clickable virtual maps.