Hi Benjamin, welcome to planDisney!
Thanks for bringing your question to us, I'm happy to help!
You can certainly visit both
Disneyland Park and
Disney California Adventure Park on the same day with one
standard theme park ticket. You will just need to add the park hopper add-on when purchasing your ticket! The park hopper add-on allows you to visit both theme parks on the same day. You will need to select which park you wish to start your day at, then you "hop" over to the second park after 1:00 p.m. (California time).
And speaking of ticket add-ons, I highly recommend you also purchase the new
Disney Genie+ Service add-on. Genie+ allows you to access the
Lightning Lane entrances for certain attractions, which should help you avoid the standby lines and save time! Another great bonus is that you get unlimited
Disney PhotoPass Digital Downloads with the purchase of Genie+. Cool right?
If you have any more questions at all, you know where to find us!
See ya real soon!
Jin