Final answer:
The event that occurred after the discovery of the Mormon Trail is the California Gold Rush, which began in 1848 and greatly influenced westward expansion in the United States.
Step-by-step explanation:
The discovery of the Mormon Trail was followed by a number of significant events. The correct answer to the question about an event that happened after the Mormon Trail discovery is b) The California Gold Rush. The California Gold Rush started in 1848 when gold was discovered at Sutter's Mill, leading to a massive influx of people seeking their fortunes. This period directly influenced the speed and scale of westward expansion and settlement in the United States.
While some of the provided options, such as the signing of the Declaration of Independence and the Battle of Gettysburg, are also important historical events, they did not occur after the discovery of the Mormon Trail. The Declaration of Independence was signed in 1776, well before the Mormon Trail came into use in the 1840s, and the Battle of Gettysburg occurred during the Civil War in 1863. The construction of the Great Wall of China dates back to