Well, I wouldn't mind it being from any of his books but I haven't read them all.
the ones I've read and own/have access to are:
The Prophet (never read), The Oath (never read) I've read the following: This Present Darkness, Piercing the Darkness, The Tombs of Aniak(sp?) and one or two of his other books for teens. I know one was about a volcanoeor something and I don't remember anything else about those last two.
"My Druid is Christ, the son of God, Christ, Son of Mary, the great Abbot..." - St. Columba “The grace of the Lord Jesus Christ, and the love of God, and the communion of the Holy Spirit, be with you all, Amen.
It looks like the common ground of 'books read' for you who have spoken up is the 'Cooper Kids' series.
*tracks down some copies and starts reading*
Okay, let's go with this question:
Jerry Frieden vanishes while exploring a hole that appears in the floor of an archaeological site that Dr. Cooper's team is excavating. What is the archaeological site at the top of the hole? (Note: Not what is at the bottom of the hole, but what is at the top.)
It was an eerie sight. Below them stretched a wide, desolate valley bordered on either side by low, sunbaked hills and rocky crags. The floor of the valley was peppered with low, bristly desert brush and scattered rocks. But in the very center of the valley, looking very unnatural, was a wide, circular area at least a quarter of a mile across in which nothing--absolutely nothing-- lived or existed. The ground inside the circle was ashen, a glistening, salty white, as if a meteor had hit or an explosion had blown everything within the circle to white, powdery dust. Furthermore, in the very center of the huge circle, the ground fell away into a deep hole, a dark, gaping cavern that looked like a sinister funnel, a bottomless whirlpool carved in rock and sand. (Dragon's Throat)
(Oh, and I have access to the Cooper family adventures and the Piercing/Present Darkness series.)