Other than Amazon and Beet Harvest, what's out there?

The hotels, restaurants and camps in Alaska all need tons of people for the season. There is a huge temp/migrant workforce that goes there each year.

Summertime in the northern states is also a time when the Utility Locating Services start hiring. This is easy to learn and you can make $18 to $25 per hour with overtime depending on experience.

Also little known is the Rail Road crew transportation industry which is usually in a constant state of hiring. Summer is the busiest time. In any large Rail Road town like Cheyenne Wy or Minot ND or Fargo ND there are companies that hire drivers to pick up and deliver RR crews to their trains. Pay here can vary wildly depending on location and can be very good or not so good.

The above with the exception of Alaska Jobs wont include any campsite.

I am not familiar with the beet harvest can someone enlighten me on that?

I can't answer directly but I like this website.