Here is a list of vegetables you can plant in March in the Las Vegas Valley. The Las Vegas Valley is around 2000 foot elevation (650 meters). Lower elevations can start earlier than this. Higher elevations can delay planting a bit.
T= tramsplants are best
s= cam be started by seed
March
Bush beans (s), broccoli (s,T), brussels sprouts (T),
cabbage (T), carrots (s), sweet corn (s), eggplant late in the month (T), green
beans (s), pole beans (s), kale (s), kohlrabi (s), lettuce (s), onion sets,
onions (T), peppers late in the month (T), potatoes, radishes (s), spinach (s),
Swiss chard (s), tomato late in the month (T), turnip (s)
cabbage (T), carrots (s), sweet corn (s), eggplant late in the month (T), green
beans (s), pole beans (s), kale (s), kohlrabi (s), lettuce (s), onion sets,
onions (T), peppers late in the month (T), potatoes, radishes (s), spinach (s),
Swiss chard (s), tomato late in the month (T), turnip (s)
Isn't it better to plant brassicas in the Fall rather than spring in Vegas? Don't most of them try to bolt pretty quick?
It depends on your microclimate in your yard. If it is hot area such as west or south facing I agree. If colder spots, north facing, east facing, shade of south walls, then it should work. I would recommend having garden beds in different locations to take advantage or these microclimates.