Hi there, Theresa!
Welcome back to the Disney Parks Moms Panel, and thanks for this great question. I love helping fellow New Mexicans plan their trips to the Happiest Place on Earth.
Halloween Time at the Disneyland Resort is my very favorite season. I just love the beautiful fall colors down Main Street, U.S.A., the transformed attractions, and the autumn-inspired treats. This season currently is set to end on October 31, 2019 which means it is possible that the giant pumpkin and fall decor may be gone on November 1, 2019. To be sure you won't miss this fantastic photo opportunity, I would recommend visiting Disneyland Park on or before October 31, 2019.
The Christmas season begins on November 8, 2019, and some festive holiday decor will start to be put in place right after Halloween Time ends. I hope that helps!
If you are utilizing One Park Per Day tickets, you can visit any park on any day. This means if you want to finish your trip in Disneyland Park, you are more than welcome to do so as well as visit it any of the other days of your trip, too! I always prefer to start and end my trips in Disneyland Park, because it's always so magical for me to say hello and goodbye to Sleeping Beauty Castle and Main Street, U.S.A., where it all began over 60 years ago with Walt himself.
I hope this helps, and please return if you have any other questions. Have a Zip-a-Dee-Doo-Dah day!
-Jennifer