The nicest and also modest hike in Yosemite Valley is from Happy Isles up the Merced River. You can choose how far up you want to go. You can make the hike as difficult as you want by going as high as you want. There are two beautiful waterfalls - Vernal and Nevada. One branch of the trail goes into the spray from Vernal Falls, called the Mist Trail.
Another very nice and short hike is to the bottom of Lower Yosemite Falls.
Zion hikes in the Valley are all short. The Narrows at the very end is a lot of fun. Another short and very good hike is the Overlook Trail, which starts along the drive toward the east exit just after you exit the tunnel. It is a special treat.
Other hikes in Zion are much longer, but tremendous.
Bryce has several short walks that go down into the formations and return back up.
I live in California and have been on these hikes. Near Bryce, I can recommend easy (and more challenging) slot canyon hikes, which are spectacular. Google “Willis Creek slot canyon” for an easy and very nice one that is easy to get to. I always recommend it.
Monument Valley is visited with Navajo Indian guides that you must hire, I think. The rules have changed for hiking there.
Page is surrounded by wonderful red rock country with countless hikes, but I would need to know more to give you advice.
The Grand Canyon is difficult for hikes because its hugely deep and very hot in Summer. One hike I always recommend is Shoshone Point. It is a level 1.6 km hike on flat land through dry woods out to the rim. It has a great view without the crowds and improvements - a more wild experience. The rim is not protected but not too dangerous there, but be careful.