The Fecund Mother

The Fecund Mother is a being of murky origins. Notes scattered around her church indicate she was once a mortal woman and daughter to a priest or otherwise 'devout' man. He father murdered her for her scandalous behaviors but she didn't stay dead and went to him again. He killed her again and his time he burnt her corpse but he was caught and hanged for her murder. He however came back to life, in some perverse way she had given birth to him.

Cult
The Fecund Mother is worshiped in Redemption Church under the guise of Kay.

The Fecund Mother
The Fecund Mother takes the form of a giant dark maw that can spit explosive spheres of something probably best not thought of. Quite what else she is and/or was is unclear but a human could be devoured by her and given a new young mortal form in return, a form of fleshy reincarnation. Her cultists were also able to create simulacra of humans and it seems unlikely that she was not in some way involved in the process.

Charles Reed manages to 'kill' The Fecund Mother and destroy most of her cult but they were still accepting donations not long after. It seems that to some extent the cult still survived, and if they did it is likely so did she....

Identification
Songs of the Horned Woods. (a sacred text to her worshipers)

''Ia ! We'll feed the Daughter of the Woods so she devours the weak flesh. Ia ! Shub-Niggurath ! A mortal man is allowed to touch the womb of the Life. Ia ! A mortal man is allowed to be reborn in a new form. Ia ! A mortal man will gain a thousand faces, a thousand eyes, and a thousand vessels for his mind.''

Shub-Niggurath is referred to in Lovecrafts works as "The Black Goat of the Woods with a Thousand Young" and more importantly in this case "Lord of the Wood". Just as Lovecraft was unclear with her identification the sinking city is vague, she is revered as a goddess but her exact status is uncertain.