Based on the information you posted, my first inclination would be to say that what you saw was a military aircraft. Since you said it seemed large and when it passed about a mile away it was loud, I would guess that what you saw was a B-1b bomber. The town you live in is just outside the boundaries of the airspace reserved for Mountain Home AFB in Idaho. Mountain Home AFB is the home of what the Air Force calls a "composite" wing of aircraft. They have fighters, bombers, tankers and other support aircraft stationed at Mt Home.
Your guess as to the distance covered in approx 30 sec may be close. The B1-b is capable of supersonic flight, you mention not hearing a sonic boom, so assuming that the aircraft was flying at a high subsonic speed that would put it at about 600-700 MPH which would mean the aircraft would cover approx 5-6 miles in a 30 second span.
I would theorize that you happened to catch a B-1 approaching from the west at first then heading to the south, preparing to do some simulated manuvers inside Mountain Home's airspace. This makes sense because Mountain Home's largest area of airspace is to the SW of your town.
B-1's are very loud aircraft, I was stationed at Grand Forks AFB in North Dakota just before they changed them over from nuclear to conventional in the early 90's so I have quite a bit of experience with them. We used to sit outside in the summer evenings and watch them take off, it's quite loud and spectacular as they light up the afterburners shooting blue flames several feet off the tail of the aircraft.
I obviously cannot tell you for sure that this is the answer behind what you saw, but I would say that this is probably the most likely answer based on the information you have given.