I visit the area several times a year as I have a sister in law and nephews there.
There was a good trail southwest of the Quail Hill area. A guy named Adam and a number of other people put a lot of effort to improve the trail. The Irvine people responded by closing the trail except for occasional escorted tours, supposedly due to wildlife considerations. The wildlife considerations were caused by building another neighborhood of housing that significantly reduced the width of the open area. I was hunted down by security for using the trail, but at least I was not arrested.
The person who works on the 16th floor at Fashion Island must be working in the basket of a balloon I have never seen. The highest buildings are at most 3 or 4 stories as best I remember. There is a balloon at the Great Park on the site of the former El Toro Marine airbase. I attended a fine free concert there a half dozen years or so ago.
As some have noted UCI has a good reputation