Ashtavinayaka sthala-purana (derived from the Mudgala Purana + Ganesha Purana)
Parvati performed a 12-year tapasya on the Lenyadri mountain to obtain Ganesha as her son; on Bhadrapada Shukla Chaturthi (Ganesh Chaturthi) she shaped a clay/uptan-oil image of Ganesha which came alive — Ganesha's birth-site; Ganesha is said to have spent his childhood (~15 years) here.
