Halloween in Santa Ana, 1894

The earliest description of a Halloween celebration in Orange County I've found so far is of a Santa Ana "Halloween Party." The following comes from the Los Angeles Times, Nov. 2, 1894 :

"A circle of young people passed a very pleasant season in the G.A.R. Hall Wednesday evening in celebrating All Saints' day. The mysteries of 'ye olden time' were delved into by the young people in a pleasant and interesting manner and many were the happy surprises enjoyed by them all. At a late hour refreshements of tamales, coffee and sandwiches, furnished and prepared by the gentlemen, were served, after which toasts were responded to by Messers. E.B. Turner, Lon Hickox and John Nourse.

It was the hour of midnight before the party, composed of the following ladies and gentlemen, departed for their homes:Misses Conley, Collins, Clara and Grace Carpenter, Flook, Mansur, Padgam, Stone, Walker, Clara and Maye Wight and Messrs. Heron, Caskey, Gould, Nourse, Chilton, Hasel, Hervey, Turner, Hickox, McIntier, Bell and Carpenter."

So,... They celebrated Halloween by eating Mexican food and staying up late talking about history. I'm a little annoyed that I didn't get to attend!
For the record, the G.A.R. (Grand Army of the Republic) Hall was on the southeast corner of Main and 4th St. (The building they held the party in is now long gone.)
Halloween itself didn't really get rolling as a holiday in America until the 1840s, when waves of Irish immigrants came to this country. Even as late as 1889, the celebration of Halloween was novel enough in Southern California that the Times saw fit to explain it to their readers:
"It is the night of all others, when spirits walk abroad, and is observe with an immense consumption of nuts and apples. The apples were once set floating in a tub of water, into which the juveniles by turn ducked their heads in order to catch one of the fruit."