Godan verb with 'ru' ending, Intransitive verb
to mix (with); to be mixed (together); to be mingled
esp. 入り交じる for people
町田は古いものと新しいものが入り交じった面白い街です。Machida is an interesting city that's a mix of the old and the new.
Also written 入り交じる【いりまじる】、入りまじる【いりまじる】