Six years after opening in a trailer in San Clemente, Mission Valley Bank finally has managed to see construction of its headquarters begin next door in what will become the Mission Valley Bank Plaza.

The bank will occupy 12,000 square feet of the 14,000-square-foot structure at the corner of Avenida Palizada and El Camino Real. Construction is expected to be completed next spring.

The plaza is a joint venture between Steve Samuelian of Emerald Development in San Juan Capistrano and four bank directors--Stewart S. Mortensen, Jack R. Barnes, Fred Debs and John Gorny. Mortensen is the bank’s chairman and Barnes is president. Each group owns 50%.

The bank sold the land to the joint venture for $1.4 million, making a gain of $500,000. The joint venture borrowed $2 million from competitor Mariner’s Bank for construction and will lease the structure back to Mission Valley Bank for a long term at market value. The joint venture would not reveal the monthly lease payment because it intends to rent the remaining space to other firms.

As of the end of August, Mission Valley Bank had earned $574,000 for the year, more than the once-sleepy bank had made in any previous year. It has about $34 million in assets.