In the American city of San Diego, there are several cryptocurrency trading platforms that cater to the growing demand for digital currency trading. Some of the popular platforms in San Diego include:

1. Coinbase: Coinbase is one of the largest and most well-known cryptocurrency exchanges in the United States. It allows users to buy, sell, and store various cryptocurrencies such as Bitcoin, Ethereum, and Litecoin. Coinbase is known for its user-friendly interface and strong security measures.

2. Kraken: Kraken is another popular cryptocurrency exchange that is based in San Francisco, but serves customers in San Diego as well. Kraken offers a wide range of cryptocurrencies for trading, as well as advanced trading features for experienced traders.

3. Binance.US: Binance.US is the American arm of the global cryptocurrency exchange Binance. It offers a wide selection of cryptocurrencies for trading and has competitive fees. Binance.US is a popular choice for traders looking to access a diverse range of digital assets.

4. Bitfinex: Bitfinex is a cryptocurrency exchange that offers advanced trading features such as margin trading and lending. It has a large selection of cryptocurrencies available for trading and is known for its high liquidity.

5. Gemini: Gemini is a cryptocurrency exchange founded by the Winklevoss twins and is known for its strong security measures and regulatory compliance. Gemini offers a range of cryptocurrencies for trading and is a popular choice for both beginner and experienced traders.

These are just a few of the cryptocurrency trading platforms available in the city of San Diego. Traders in the area have a variety of options to choose from based on their trading needs and preferences. As the popularity of cryptocurrencies continues to grow, it is likely that more trading platforms will emerge in San Diego to meet the demand for digital currency trading.