Great Valley of California. 279 
ı. Original coastwise vegetation (now on islands and mainland). 
2. Mountain forests. 
3. Chaparral. 
4. Boreal-alpine plants on mountain summits. 
5. Desert and Great Valley vegetation. 
With increased elevation and the exposure of fresh areas to invasion desert 
species moved into the arid regions and grasses and other plants into moister 
situations to form the grass-land and tule formations of the great San Joaquin 
valley and other smaller valleys, that owe their soils to a delta formation. 
Great Valley of California. The Great valley of California, which lies 
between the Sierra Nevada Mountains on the east and the Coast ranges on 
the west, is an alluvial plain with little departure from a monotonous level 
surface. It includes three basins of drainage called respectively Sacramento 
valley (northern), San Joaquin valley (southern) and the depression of Tulare 
Lake. From the orogenic disturbance at the close of the Miocene, when the 
Coast ranges appeared as a connected mountain chain dates the history of 
the Great valley. During the Neocene, the Great valley was occupied by a 
gulf, connecting with the ocean by one or more sounds across the Coast 
ranges. During Pleistocene times, the Great valley was finally cut off from 
the sea. The elevation of mountains closed in the valley which became a 
well defined area of sedimentation, or deposit. With the surface of the ground 
only 46 feet above sea-level, the occurrence of logs of wood at 349 feet, 
recent shells up to 600 feet can only be thus accounted for by subsidence 
and deposition, when sediments 2000 feet in thickness were formed. The Great 
valley is, therefore, an example of a well defined area of progressive sub- 
Sidence associated with heavy accumulations of sediments. 
A flora older than that of the plain flora of the valley consists of the 
formations which are found in the tule swamps, or marshy areas which Ber 
the rivers for a considerable distance on either bank. The Sacramento River 
is bounded by brackish marshes for 150 miles from its mouth which stretch 
away from the river ten to fifteen miles on either hand. These marshes are 
Commonly referred to as tule lands. Along the new and old river ‚channels 
the deposition of sediments has built up natural levees with brackish water 
back of them where waving masses of tule (Seerpus lacustris var. occidentalis) 
Occur. 
The following trees and shrubs fringe the water ways '). 
Salix nigra Marsh, ° | Platanus racemosa Nutt. 
° lasiandra Benth. | Populus Fremontü Wats. 
° longifolia Muhl. Cephalanthus occidentalis E 
°  sessilifolia Nutt. Fraxinus oregana Nutt. 
: 238. 
un 1) JePson, Wirus L.: The riparian Botany of the lower Sacramento. Erythea I, 1893: 23 
NDEGEE, K.: Flora of Bouldin Island. Zoe IV: 212. 
