US Post Office is located at 3101 W Sunflower Ave, Santa Ana, CA. This location is in the South Harbor neighborhood. This business specializes in Post Offices. US Post Office is open Mon, 6:05am-7pm; Tue, 6:05am-7pm; Wed, 6:05am-7pm; Thu, 6:05am-7pm; Fri, 6:05am-7pm; Sat, 8:05am-3pm; Sun, Closed and accepts American Express, Discover, Mastercard and Visa.