At least, the first reported in the Los Angeles Times as far as my Proquest search is concerned.
The April 2nd, 1885 edition of the paper says that a reporter from the Herald and "the whole reportorial corps of the Express" trotted out to Sonoratown when told (by telephone) of a suicide in a bar called the Monkey Saloon.
Apparently the Monkey Saloon was real, because everyone knew where to find it. A couple of off-duty cops showed up as well, and the deputy coroner got half-way there before learning the call was bogus.
The intrepid journalist from the Times knew better and stayed home...wonder if he had anything to do with the joke?
Anyhow, the corpse turned out to be made of straw. Big laugh. As the Times reported, "The only parties who really suffered from the canard were the unfortunate Express reporters, as it came at the busy time of the day for them, and, fatigued and unhappy, they returned to their unfinished duties."
Just where was Sonoratown in 1885? Believe it or not, googling the place with Los Angeles led me to this 1885 photo at the LA History Galley (sometimes life is so easy!)
This photograph is credited to a bicentennial-era book, A Guide to Historic Places in Los Angeles County, edited by Judson Grenier.
The site says that Sonoratown was located north of Old Sunset, east of Buena Vista, and west of North Main. My good ol' Los Angeles A to Z: An Encyclopedia of the City and County by the Pitts puts Sonoratown along North Main and North Broadway "and on the hilly streets north and west of the Plaza, including Alpine and Buena Vista." The residential neighborhood existed from the 1850s till the early 1900s.