ROCK PARAPET--Approximately 200 years ago prevailing climatic conditions
were of such nature as to permit germination of a large number of
Saguaro seeds, creating the more or less even-aged stand of Giant
Saguaros we see here today.
The Tanque Verde Mountains to the east are composed largely of
crystalline rocks formed under conditions of great heat and pressure.
They were elevated by movements of the earth's crust and now are
gradually being eroded away.
The Tucson Valley to the north is in reality a deep canyon (2,000 to
3,000 feet) filled with debris.