Until 1972, houses in Butterfly Hollow had septic tanks. Ours nourished five species of native trees, whose measurements indicated that they grew at twice the forest's normal rates. But the human population of my suburb doubled in size during the 1960s and 1970s, which meant that too many septic tanks seeped too much polluted water into creeks, which drained into a reservoir that was another city's water supply. Eventually, a regional sewer system was built with neighborhood pipes under streets and collector lines in the ravine. Ditches dug for the new lines damaged reforestation temporarily but reviewed scenes over past runs of the play.

Ridgetop ditches had two to three inches of dark brown organic soil above a foot of light tan chips and small flakes of limestone overlying a foot and a half of larger slabs and rock chunks. That was the root zone for most plants. In the ravine bottom, however, the six- to eight-foot-deep ditch sliced through a creek-made "layer cake" of angular rock chips alternating with soil, signifying respective periods of slope erosion alternating with quieter water. Tree roots grew throughout the profile with growth rings in their cut ends, indicating that the exposed layer cake was three centuries old, recent erosion coincided with suburban sprawl, and forest giants remembered a deeper ravine in a quieter time.