PHYTOGEOGRAPHY OF MANOA VALLEY, HAWAIIAN ISLANDS 585 
3. A series of cliffs or palis, which He between the ridges, and are more 
or less covered with vegetation. These cliffs are 200-300 feet 
high, and are cut at fairly regular intervals by V-shaped gorges 
and hanging valleys, from the mouths of which waterfalls issue 
and drop down the face of the cliffs. 
4. Above the cliffs is a series of hanging valleys, separated from one 
another by steep ridges. These ravines have an average eleva- 
tion of 1,400-2,000 feet and open above the face of the precipice. 
They extend abruptly back and up to the main summit ridge, a 
distance of .50-. 75 mile. 
5. The summit ridge. 
Fig. 9. /Typical physiography of valley head, summit ridge and peaks. Note 
ravines and hanging valley formation. 
The general structure of Manoa Valley, with reference to plant 
geography, is fundamentally the same as that of the other valleys 
along the leeward flanks of the Koolaus. However, variations of 
marked phytogeographic significance may be noted. Nuuanu Valley, 
for example, has cut completely through the range, and so its head is 
much more windswept than that of Manoa. The difference in the 
windiness of the heads of these two valleys has produced an observable 
difference in their respective vegetations, that of Nuuanu being 
