Colegio Las Cumbres provides a summary of the content covered in their senior writing course over the three trimesters. The first trimester focuses on describing people and places through adjectives, adverbs, prepositions, and connectors. The second trimester covers writing letters, revising language, and paragraph structure. Students also work on short story elements like plot development and topic sentences. The third trimester emphasizes writing short stories and further developing descriptive techniques.