Oceanside, California is 60% larger than Boulder, Colorado.
Area: 68 km2 calculated
Boulder is the county seat and most populous city of Boulder County and the 11th most populous city in the U.S. state of Colorado. Boulder is located at the base of the foothills of the Rocky Mountains at an elevation of 5,430 feet. The city is 25 miles northwest of Denver. Wikipedia
Area: 108 km2 calculated
Oceanside is a coastal city located on California's South Coast. It is the third-largest city in San Diego County, California. The city had a population of 183,095 at the 2010 census. Together with Carlsbad and Vista, it forms a tri-city area. Wikipedia