APA (7th ed.) Citation

Yard, R. S. (2008). The Book of the National Parks. Project Gutenberg.

Chicago Style (17th ed.) Citation

Yard, Robert Sterling. The Book of the National Parks. Project Gutenberg, 2008.

MLA (9th ed.) Citation

Yard, Robert Sterling. The Book of the National Parks. Project Gutenberg, 2008.

Warning: These citations may not always be 100% accurate.