>>614010Those are just cumulus. Cumulonimbus are more dense and vertically extensive.
>>614012Anvil tops occur when the towering cumulus reach the tropopause and hit an inversion layer in the stratosphere. A stable atmosphere (such as in the stratosphere) inhibits the thunderstorm from developing vertically, so it flattens out.
Here are some later afternoon thunderheads that have formed in the Eastern Sierras
