Buses dropped off hundreds of migrants at a San Diego bus stop instead of at a reception center that had been serving as a staging area because it ran out of local funding sooner than expected. The deposits Friday of immigrants from countries as far away as Mauritania, China and Ecuador show how even the largest city on the country’s southern border is struggling to cope with the unprecedented influx of people. The buses brought the migrants to the reception area, where migrant aid groups said they would be taken to another place to charge their phones, wash faces and use a bathroom. The vast majority planned to spend only a few hours in San Diego before heading elsewhere.