This was a great hike in the Saguaro National Park!  Despite it being the longest hike, we actually thought it was our easiest hike so far (we've done Piestewa and Picacho up to this point).  The scenery was incredible with a lot of saguaros (not a surprise) but we did encounter something unusual on the way up.  We decided to take the loop on one side, go to the summit and then continue the loop on the other side back to the car.  On the way up, we heard  a loud boom and the earth shook below us.  At first I was thinking earthquake but couldn't explain the sound.  Another hiker on the trail said he thought it was a sonic boom.  We could see for miles in all directions but there was no sign of a military jet in sight (we looked around thinking the sound may have been lagging the location of the jet).  If anyone else was hiking this day, we would love to get your thoughts.  My guess is this was between 10-11am.