30 



the mountains where they terminate in ahnost vertical cor- 

 rugated walls. Lualualei, Waianae and Makaha are the most 

 prominent of these valleys. Kaala peak, back of Waianae 

 valley, elevation 4040 feet, is the highest point on Oahu. 



"The Koolau mountains came into being long after the ^^"ai- 

 anae mountains. They were built up by successive lava flows 

 which, on the west, overlapped the eastern slopes of Waianae 

 and filled up its valleys. As soon as the Koolau range had 

 reached a sufficient height it formed a wind barrier in the path 

 of the trades, which largely robbed the clouds of their moist- 

 ure before they reached the Waianae mountains, so that there- 

 after the rainfall in these mountains became much less, with 

 the result that the denuding agencies also became less active. 

 The Koolau Range not only protects the Waianae mountains 

 on the west but is in turn shielded by them from the severe 

 kona storms that come from the southwest. The extent of 

 this protection is well shown by the great difference in erosion 

 on the western and southern slopes of the Koolau mountains, 

 On the south the slopes are unprotected, with the result that 

 deep, broad valleys, such as Palolo, Manoa, Nuuanu and Ka- 

 lihi, all back of Honolulu, have eaten their way into the very 

 core of the range. Indeed, Nuuanu and Kalihi have cut 

 through the core forming the low pass at the head of each 

 valley. 



"The eastern side of Ivoolau range is very much unlike the 

 western side. It is divided into two parts by the Kualoa ridge, 

 or spur, which juts out from the middle of the main range as 

 a sort of headland north of Waikane. Xorth of Kualoa arc 

 several deep valleys which extend well back into the range 

 and are separated from each other by spur ridges that branch 

 off from the main range. The valleys and ridges have prob- 

 ably resulted entirely from erosion. South of Kualoa the spur 

 ridges separating the different, valleys are almost entirely 

 wanting. The result is that the heads of the various short al- 

 cove valleys form an almost continuous corrugated wall or 

 precipice. 3 or 4 miles from shore. 1000 to 1200 feet high and 

 10 or 12 miles long. The area between the sea and the base 

 of the cliffs is comparatively open rolling country across which 

 short streams course to the sea. The existing cliff forms may 

 be due entirely to erosion, as maintained bv some authorities, 

 Vv^holly subaerial or partly submarine, or they may have orig- 

 inated in a long fissure, as suggested by Dana, which resulted 

 in a mass east of the rupture sliding into the sea. As bearing 

 on Dana's theory, it is interes<:ing to note that practically all 

 the streams south of Kualoa seem to originate in constant high 

 level springs wliich are about 1000 feet above the sea back 

 of \\'aikane and A\'aiahole and decrease in elevation toward 

 the south. These springs aj^pear to emerge from porous strata 



