Sage Narada cast off his quill to find a suitable place to perform puja to free the gods from Brahma's curse. 
The place where it landed was chosen to perform the Moksha Puja. Thus there is a popular legend that the land where Narada's Valkalam fell was called Varkala, and that the place chosen to perform the Papanasam rituals was the Papanasam Kadaltheeram.