we sent nbc bay area's kimberly terry to sun valley mall in concord to find out. is it crowded out there? >> reporter: it is crowded out there. you can see the entrance here which is not very crowded, but i do assure you there are a lot of people inside. it is crowded. the parking lots are jammed out here. yesterday, people opened up their presents on christmas, today many are here returning them. stores are just hoping those shoppers stick around to spend their gift cards and also take advantage of any post-holiday deals. christmas has come and gone, but now comes the after-christmas sales. on the holiday merchandise that didn't sell. ♪ good tidings for christmas and a happy new year ♪ >> reporter: the day after christmas has become one of the busiest shopping days of the year for retailers. >> the line was all the way out to this way, the store. >> customers that are looking for bargains, customers that are spending the gift cards that they got for christmas. and cusmers that are exchanging gifts. so there's a lot of different things going on and adds up to a bu