terms, the process of soil recovery 
would have begun as the rains leached 
out adsorbed acids. The first plant re- 
coionization was probably by lichens, 
followed by grasses and ferns, and fi- 
nally, by bushes and trees. 
Evidence of human resettlement in 
El Salvador is dramatically preserved 
at Ceren, a Pompeii-like site that I be- 
gan excavating in 1978 as part of a mul- 
tidisciplinary research team. Ceren lies 
in the Zapotitan Valley, some twenty- 
five miles northwest of Ilopango. Peo- 
ple deserted the valley when Ilopango 
buried it in about six feet of ash. Ironi- 
cally, about a.d. 600, only a short while 
after the area was finally resettled, a lo- 
cal volcanic eruption buried part of the 
valley once again, freezing the land- 
scape and society in time. 
Laguna Caldera, the volcano that 
buried Ceren the second time, is less 
than a mile north of the site. In contrast 
with Ilopango, its eruption in 600 cov- 
ered only a small area — about eight 
square miles — with a deep layer of vol- 
canic ash. The long-term cultural ef- 
fects of Laguna Caldera’s eruption 
were therefore negligible in contrast to 
the Ilopango eruption, but the event 
was a boon to those of us who seek to 
reconstruct past ways of life. This is be- 
cause the layers of tephra that Laguna 
Caldera deposited across the local 
countryside had excellent preservative 
characteristics. First, a fine-grained 
tephra fell with moisture in it, packing 
around the leaves of growing corn 
plants, around the leaves and trunks of 
trees, and around grasses and other 
plants. What is left is a cast of the vege- 
tation, and preservation is so detailed 
that even cellular structures in the corn 
plants can be observed under a micro- 
scope. The fine-grained layer, some six 
inches thick, was closely followed by a 
thinner, hot deposit of cinders and lava 
bombs. Richard Hoblitt of the U.S. 
Geological Survey in Denver has deter- 
mined, by a complicated analytic tech- 
nique involving remnant magnetism, 
that the hot layer fell at a temperature 
over 1,000°F, which had the effect of 
baking much of the buried vegetal ma- 
terials, carbonizing and thus preserving 
them. Within a few months, additional 
layers of tephra accumulated, so that 
the total depth of ash at Ceren is be- 
tween twelve and twenty feet. 
Our excavation at Ceren shows that 
