ISOSEISMALS: DISTRIBUTION OF APPARENT INTENSITY. 229 
The blocks between the old tide-marsh area, extending east from near the Post-office, 
and the former course of Mission Creek, give evidence in the form of cracked foundation 
walls, broken concrete cellar floors, etc., of intensity values high in Grade C. The fire 
did much to destroy evidence here, as it was a district of wooden dwellings. 
From near the corner of Third and King, to the corner of Folsom and Steuart Streets, 
there is a narrow fringe of land constituting the water-front around Rincon Point. The 
land is partly natural and partly made. Few structures are found on it which are not 
built on piling, whether they be warehouses on the docks or good modern buildings. Some 
parts of the area are devoid of buildings. No evidence was disclosed in this tract indicat- 
ing intensity higher than Grade C. Significant evidence was scarce. Cracked brick 
walls here and there served to fix the degree of intensity. 
Onward to the north and to the west from the corner of Steuart and Folsom Streets, 
extends a narrow sinuous area around Telegraph Hill to the vicinity of Black Point, 
which is designated upon the map as affected by an intensity of Grade C. Such effects 
as badly cracked brick walls, some of which fell, the fall of cornices and gables, ete., 
are said to have been developed here. Such evidence as could be made out amid the 
fire ruins tends to confirm this. This region divides the water-front area of made land, 
where high intensity was developed, from sandstone hills, where a lesser shock was ex- 
perienced. It will be discust further in connection with phenomena of special significance. 
A low-lying crescent-shaped area of alluvium and sand, with a little made land near the 
shore, extends westward from Black Point to Fort Point. South, east, and west the 
hills rise steeply. Formerly a tide-marsh completely separated the alluvial flats from the 
sandbar at the shore. Part of this,near its mouth, has been filled. Buildings are scantily 
distributed all over the area. Evidence in the form of structural damage is not, therefore, 
met frequently. The filled land of the tide-marsh is devoid of structures. There are 
several little localities in this district marked by damage denoting intensity of Grade B. 
These will be mentioned later. For the most part, frame buildings occasionally tilted a 
little out of the vertical, and cracked and crusht foundation walls are typical of the de- 
structive effects found here. 
Leading down into this area from near the corner of Polk Street and Pacific Avenue 
is a minor valley, once deeply trenched, but now modified by alluvial and artificial filling. 
Along its course most chimneys were thrown and foundation walls were cracked and crusht 
generally. Two little places, where intensity of Grade B was developed, are situated in 
the trough. They are discust below. 
A group of small areas, 4 in number, together with a small spur of Mission Valley, 
situated along a line extending northwest from about the junction of Sixteenth and Dolores 
Streets, is designated upon the map as characterized by intensity of Grade C. It chances 
that the northwest extremity of this line coincides with the location of an old fault-zone, 
mentioned above as partly determining the southwestern limits of the serpentine. 
In one of these localities, practically bounded by Maple, Spruce, Washington, and 
California Streets, brick walls and foundations were cracked conspicuously. A building 
at the corner of Maple and Washington Streets had a balcony supported by pillars above 
its front entrance. This was thrown down, and the walls were cracked rather badly. 
It was probably a structure ill adapted to resist earthquake shock. Still it.stands directly 
upon a bare ledge of serpentine, and upon similar rock in the Potrero, an equal distance 
from the fault, intensity of only Grade EK was developed. 
At the corner of Maple and California Streets, the Hahnemann Hospital, a new brick 
building, sustained severe damage, particularly the east wing. If neighboring structures 
showed any destructive effects comparable with this, intensity of Grade B would be in- 
dicated. But they do not. Some cause peculiar to the building itself is responsible for 
the exaggeration of the intensity. Probably the newness of the masonry was a contribu- 
tory factor. The surface material here is sand, but it can not be very thick. 
