Where was sea level during the last glacial maximum (say if sea level
were 150 m lower than today) in southern california? I'm looking for
recent (made in past 20 years) bathymetric map(s) of southern
california between San Diego and Los Angeles to answer this question.

Hello there

From the way your question is worded, I would guess that you are
looking for oceanic 'bathtub rings,' giving evidence of past sea
levels.  This same kind of information is also of interest to
archaeologists when we study coastal history and settlement patterns.

This page has a click-to-enlarge bathometric map (fig 2) of the
Southern California seabed.  They say the map is 'new' and the
information is dated July 01.
http://www.oar.noaa.gov/spotlite/archive/spot_faults.html - "Submarine
Faults of the San Andreas: Southern California's Hidden Hazards"

Here you will find a click-to-enlarge multibeam bathymetric map of the
floor of Santa Monica Bay which would be at the northern end of your
interest zone.
http://soundwaves.usgs.gov/2000/02/fieldwork.html - From USGS

This map begins as a global image.  Click on a 45 degree by 45 degree
square to zoom in, then click on the image that comes up to see a
full-resolution image.
http://www.ngdc.noaa.gov/mgg/image/2minrelief.html - "NGDC/WDC MGG,
Boulder - 2 minute bathymetry/topography image selector"

Here is the GEBCO CHART for SEAFLOOR from SAN FRANCISCO to BAJA shows
seafloor off San Diego [General Bathymetric Chart of the Oceans, 1984,
Intl Hydrographic Orgn]
http://scilib.ucsd.edu/sio/ocean/gebco.jpg - From University of
California, San Diego

If you wish to purchase a CD bathometric map of the southern
California coast - "3 arc-second gridded bathymetry data merged with
USGS 3 arc-second topo data. Volume 6 covers the Southern California
Coast between latitudes 32-37.
Contact: David.Divins@noaa.gov or 303 497-6505. 
http://oas.ngdc.noaa.gov/ngdc/plsql/ngdc_products.disc_prods?disc=G05
- National Geophysical Data Center

This next website I am sending you to may even have the answers you
are trying to research.  As a retired archaeologist, I often look in
that direction to find information which may seem otherwise entirely
unrelated.

Here you will find maps of the California coastline and channel
islands along with sea level information for conditions as they were
10,000 - 12,000 years ago.   Things were vastly different than they
are today.  You will find maps and full explanation as to how the
research was completed.  It is a PDF file so you will need Acrobat
Reader.
http://www.pcas.org/Vol35N23/3523Porcasi.pdf - "Early Holocene
Coastlines of the California Bight" - From Pacific Coast
Archaeological Society Quarterly

I hope the above is of help.

Search - google
Terms - bathymetric map/s southern california coast, bathymetrioc
charts, seabed contour map/s, seabed contour charts

If I may clarify anything, please ask before rating answer.

Cheers
digsalot