You can do something like this, but very likely you might need to refine the regex pattern for your actual application.
library(tidyverse)
large_dataset <- data.frame(stringsAsFactors = FALSE,
EA = c("Los Angeles, CA", "Other text")
)
large_dataset %>%
filter(str_detect(EA, pattern = "CA"))
#> EA
#> 1 Los Angeles, CA
Created on 2019-11-22 by the reprex package (v0.3.0.9000)