The legend started in 1938 when Southern California had 14 days of rain causing sever flooding. Here is part of the article from the Santa Ana Register (now the OC Register)

 

Corona, CA -- AP
As the flood waters subside from 2 week of flooding, 13 coffins were
discovered in the wooded area next to River Rd  and Archibald Ave in
the city of Corona. "The coffins are believed to from the abandoned
Guasti Cemetery in the city Ontario" said Officer Willmans. Officer
Willmans went on to say "The coffins were found by some locals floating
in a small creek that runs through the woods. The authority's and
locals started referring to this area as Coffin Creek.

The authority's continue to search the woods for the remains of the 13
coffins. Only 2  coffins had the remains found nearby. The remains of 2
other empty coffins were found in the woods, some 30 yards to the west
of what is now called Coffin Creek.

As the sun rose, Officer Willmans said " We had to stop searching
last night, those woods got really creepy after dark. I called off the
search when I started seeing and hearings things, strange things, like
(continued on page 3 see Coffin Creek)

 

This is all of the article I could find, page 3 was missing. Now it's up to you to find out what is haunting the woods.