Is I Know Why the Caged Bird Sings copyright or public domain?

I Know Why the Caged Bird Sings is currently still under copyright. Under current US copyright law, the 1969 book is a protected work. If Ms. Angelou were to die today, I Know Why the Caged Bird Sings would not enter the public domain until midnight the end of the calendar year, 70 years past the death of the author.