This is the California Free Digital Calculus Textbook by David R. Guichard and other contributors.

This book is in use at Whitman College and is occasionally updated to correct errors and add new material; the latest version can be found at www.whitman.edu/mathematics/calculus.

If you are interested in the multivariable version of the book, it is at www.whitman.edu/mathematics/multivariable.