Click in the Eyewitness News story window above to watch the accompanying video to this story.
Neighbor Jesus Vega said he thought it was a doll at first when he looked out his window. His neighbor, who lives on the property where the body was discovered, told him it looked like a newborn.
"The dog that belonged to the property here was lying next to the baby on the ground," said Corp. Jose Gonzalez of the Santa Ana Police Department.
Police said it does not appear as though the body was buried, and it also does not look like the dog dug it up and carried it.
"There is an alleyway that is accessible from the rear of property, so it is quite possible someone may have disposed of body by simply throwing it over that fence," Gonzalez said.
Neighbors said one family owns both homes, and a number of family members live in each house. Authorities questioned family members Monday, but they told police no one was pregnant, and they did not know how the baby got there.
Anyone with information is urged call the Santa Ana Police Department at (714) 245-8665.